Magnetic recording medium and method of producing the same

ABSTRACT

The present invention provides a method for manufacturing a magnetic recording medium comprising the steps of forming a carbon protective film onto a disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, wherein a mixed gas of hydrocarbon and hydrogen, in which the mixing ratio of hydrocarbon to hydrogen is in the range of 2 to 1˜1 to 100 by volume, is used as a reactant gas, during bias applying to said disc. In addition, the present invention provides a magnetic recording medium comprising a carbon protective film formed onto a disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, wherein said carbon protective film is formed according to a plasma CVD method, while applying bias.

TECHNICAL FIELD

The present invention relates to a magnetic recording medium such as amagnetic disc and the like for use in magnetic disc devices, and amanufacturing method for the same.

RELEVANT ART

In recent years, in the field of magnetic recording, particularly withrespect to magnetic discs, remarkable improvements in the recordingdensity have been achieved. In particular, recent improvements in therecording density have continued at a phenomenal pace, achieving ratesof approximately 100 times in 10 years. Technologies supporting theimprovement of recording density vary widely, however, one of the keyconcepts that can be mentioned is the technology of controlling thesliding characteristics between the magnetic head and magnetic recordingmedium.

Sliding of the head on the medium is unavoidable ever since theintroduction of the CSS (Contact-Start-Stop) mode which is so-called“Winchester format” as the main mode for hard disc drives, wherein thebasic operation comprises the steps of sliding into contact, headflotation, and sliding into contact between the magnetic head andmagnetic recording medium. Accordingly, problems relating to tribologybetween head and medium have become critical technical problems. Thus,properties such as resistance to abrasion and resistance to sliding overthe surface of the magnetic recording medium comprise the keys to areliable product, and efforts continue to develop and improve theprotective film, lubricating film, and the like, which coat the magneticfilm.

As a protective film for magnetic recording medium, films comprisingvarious materials have been proposed. However, from the perspective ofthe total performance such as coating performance and durability, carbonfilms are principally employed.

These carbon films are generally formed according to a spatter-coatingmethod, in which the coating conditions are extremely important due totheir direct impact on resistance to corrosion and CSS properties.

In addition, in order to improve the recording density, it is preferableto reduce the flying height of the head, to increase the number ofrotations of the medium, and the like. Thus, a superior resistance tosliding is required for the magnetic recording medium. On the otherhand, in order to improve the recording density by means of reducingspacing loss, it's preferable to make the protective film thinner, forexample to a thickness of 100 Å or less. Hence, a thin, smooth anddurable protective film is highly desired.

However, a carbon protective film formed according to the conventionalspattering coating method, can sometimes lack durability, when the filmis made thin, for example 100 Å or less.

Therefore, a plasma CVD method is currently being studied as a methodfor providing a carbon protective film with greater strength, comparedto that produced by means of the spatter-coating method. This plasma CVDmethod is disclosed in, for example, Japanese Patent Application, SecondPublication No. Hei 7-21858; First Publication Laid Open No. 7-73454;and the like.

However, under the current demands for increased recording density, itis difficult, from the perspective of durability to sliding, to producea thin protective film to the point where a sufficiently high recordingdensity is achieved without lowering the output properties, according tothe aforementioned conventional technology. In addition, theconventional technology poses the problem of low coating rate, which inturn leads to production inefficiency.

In consideration of the aforementioned, the objectives of the presentinvention are described as follows.

(1) To provide a magnetic recording medium and manufacturing methodthereof, that is reliable and capable of providing a sufficiently highrecording density, without lowering the output properties.

(2) To provide a method for manufacturing the aforementioned magneticrecording medium in an efficient manner.

DISCLOSURE OF THE INVENTION

The method for manufacturing a magnetic recording medium according tothe present invention comprises a method for manufacturing a magneticrecording medium by means of forming a carbon protective film onto thedisc, the non-magnetic substrate of which is layered with a non-magneticbase film and magnetic film, using a reactant gas containing carbonatoms as a starting material, according to a plasma CVD method, whereina mixed gas of hydrocarbon and hydrogen, in which the mixing ratio ofhydrocarbon to hydrogen is in the range of 2 to 1˜1 to 100 by volume, isused as a reactant gas, while applying a bias to said disc.

The aforementioned hydrocarbon preferably comprises at least one type ofhydrocarbon selected from among lower saturated hydrocarbons, lowerunsaturated hydrocarbons, and lower cyclic hydrocarbons, and morepreferably comprises toluene.

In the case of using toluene, toluene and hydrogen are mixed, with amixing ratio of toluene to hydrogen preferably in the range of 1 to 15˜1to 20 by volume.

The bias applied to the disc is preferably a high frequency bias.

In addition, formation of a carbon protective film is preferably carriedout under high frequency electrical discharge.

When forming a carbon protective film on both sides of the disc at thesame time, it is preferable to make the phases of electrical powersupplied to each electrode arranged on the respective sides of theaforementioned disc different from each other. The phase difference ofelectrical power supplied to each electrode is preferably in the rangeof 90˜270°, and in particular, more preferably the opposite phase (i.e.,180°).

The method for manufacturing a magnetic recording medium according tothe present invention may comprise a method for manufacturing a magneticrecording medium by means of forming a carbon protective film onto thedisc the non-magnetic substrate of which is layered with a non-magneticbase film and magnetic film, using a reactant gas containing carbonatoms as a starting material, according to a plasma CVD method, whereinpulse D.C. bias having a frequency of 1 kHz˜100 GHz and pulse width of 1ns˜500 μs is applied to the disc, when forming (during formation of) thecarbon protective film.

The frequency of the pulse D.C. bias applied to the disc is preferablyin the range of 10 kHz˜1 GHz, and the pulse width is preferably in therange of 10 ns˜50 μs.

The average voltage of the pulse D.C. bias applied to the disc ispreferably in the range of −400˜−10V.

The aforementioned reactant gas is preferably a mixed gas of hydrocarbonand hydrogen, with a mixing ratio of hydrocarbon to hydrogen in therange of 2 to 1˜1 to 100 by volume. The hydrocarbon preferably comprisesat least one type of hydrocarbon selected from among lower saturatedhydrocarbons, lower unsaturated hydrocarbons, and lower cyclichydrocarbons.

The magnetic recording medium according to the present invention isprovided with a carbon protective film onto the disc, the non-magneticsubstrate of which is layered with a non-magnetic base film and magneticfilm, that can be formed according to a plasma CVD method while applyingpulse D.C. bias having a frequency of 1 kHz˜100 GHz and pulse width of 1ns˜500 μs to the disc.

The method for manufacturing a magnetic recording medium according tothe present invention may comprise a method for manufacturing a magneticrecording medium by means of forming a carbon protective film onto thedisc, the non-magnetic substrate of which is layered with a non-magneticbase film and magnetic film, using a reactant gas containing carbonatoms as a starting material, according to a plasma CVD method, whereinthe temperature of the disc is heated to 100˜250° C. prior to formingthe aforementioned carbon protective film.

The temperature of the disc is preferably in the range of 150˜200° C.

The aforementioned reactant gas is preferably a mixed gas of hydrocarbonand hydrogen, with a mixing ratio of hydrocarbon to hydrogen in therange of 2 to 1˜1 to 100 by volume, wherein the hydrocarbon mixed intothe reactant gas preferably comprises at least one type of hydrocarbonselected from among lower saturated hydrocarbons, lower unsaturatedhydrocarbons, and lower cyclic hydrocarbons.

The pressure of the reactant gas is in the range of 0.1˜10 Pa, andpreferably 2˜6 Pa, when forming the carbon protective film in the methodfor manufacturing a magnetic recording medium according to the presentinvention.

The aforementioned reactant gas is preferably a mixed gas of hydrocarbonand hydrogen, with a mixing ratio of hydrocarbon to hydrogen in therange of 2 to 1˜1 to 100 by volume, wherein the hydrocarbon mixed intothe reactant gas preferably comprises at least one type of hydrocarbonselected from among lower saturated hydrocarbons, lower unsaturatedhydrocarbons, and lower cyclic hydrocarbons.

The method for manufacturing a magnetic recording medium according tothe present invention may comprise a method for manufacturing a magneticrecording medium by means of forming a carbon protective film onto thedisc, the non-magnetic substrate of which is layered with a non-magneticbase film and magnetic film, using a reactant gas containing carbonatoms as a starting material, according to a plasma CVD method, whereinthe reactant gas is a mixed gas of hydrocarbon and hydrogen, with amixing ratio of hydrocarbon to hydrogen in the range of 2 to 1˜1 to 100by volume, into which nitrogen gas is added at a adding volume of0.1˜100% of the mixed gas.

The aforementioned hydrocarbon preferably comprises at least one type ofhydrocarbon selected from among lower saturated hydrocarbons, lowerunsaturated hydrocarbons, and lower cyclic hydrocarbons.

The magnetic recording medium according to the present invention maycomprise a non-magnetic substrate, layered with a non-magnetic basefilm, magnetic film, carbon protective film, and lubricating film;wherein said carbon protective film comprises a plasma CVD carbon layerformed according to a plasma CVD method, and a spatter carbon layerformed according to a spattering coating method, which lies in contactwith the lubricating film.

The thickness of the spatter carbon layer is in the range of 5˜100 Å,and preferably 30˜100 Å, and the thickness of a plasma CVD carbon layeris preferably in the range of 30˜100 Å.

In addition, the method for manufacturing a magnetic recording mediummay comprise the steps of forming (1) a plasma CVD carbon layer, using areactant gas containing carbon atoms as a starting material, accordingto a plasma CVD method; (2) a spatter carbon layer thereon, using aspatter gas, according to a spatter-coating method; and (3) alubricating film thereon, which lies in contact with said spatter carbonlayer.

The reactant gas used for forming a plasma CVD carbon layer according toa plasma CVD method is preferably a mixed gas of hydrocarbon andhydrogen, with a mixing ratio of hydrocarbon to hydrogen in the range of2 to 1˜1 to 100 by volume, wherein the hydrocarbon preferably comprisesat least one type of hydrocarbon selected from among lower saturatedhydrocarbons, lower unsaturated hydrocarbons, and lower cyclichydrocarbons.

The spatter gas used for forming a spatter carbon layer according to thespatter-coating method is preferably argon, into which at least one gasselected from among nitrogen, hydrogen, and methane, is added at amixing ratio to the argon of 0.1˜100% by volume.

In addition, the method for manufacturing a magnetic recording mediumaccording to the present invention may comprise a method formanufacturing a magnetic recording medium by means of forming a carbonprotective film on a disc, the non-magnetic substrate of which islayered with a non-magnetic base film and magnetic film, using areactant gas containing carbon atoms as a starting material, accordingto a plasma CVD method, and lubricating film thereon, which lies incontact with the carbon protective film, wherein said films are formedwhile performing bias applying to the disc, with subsequent films formedwithout bias applying to the disc.

The bias applied to the disc is preferably a pulse D.C. bias of−400˜−10V, or a high frequency bias of 10˜300 W.

The thickness of the carbon layer which is formed without bias applyingto the disc is preferably in the range of 5˜20 Å.

The aforementioned reactant gas is preferably a mixed gas of hydrocarbonand hydrogen, with a mixing ratio of hydrocarbon to hydrogen in therange of 2 to 1˜1 to 100 by volume, wherein the hydrocarbon preferablycomprises at least one type of hydrocarbon selected from among lowersaturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclichydrocarbons.

In addition, the magnetic recording medium according to the presentinvention may comprise a carbon protective film and a lubricating filmon a disc, the non-magnetic substrate of which is layered with anon-magnetic base film and magnetic film; wherein the carbon protectivefilm comprises a first carbon layer, that is formed according to aplasma CVD method while performing bias applying to the disc, and asecond carbon layer, which lies in contact with the lubricating film,that is formed according to a plasma CVD method without bias applying tothe disc.

The thickness of the second carbon layer is preferably in the range of5˜20 Å.

In addition, the magnetic recording medium according to the presentinvention may comprise a non-magnetic base film, magnetic film,protective film, and lubricating film on the non-magnetic substrate;wherein the protective film comprises a carbon layer, principallycomprising carbon, on a tantalum nitrogen layer, comprising tantalum andnitrogen with a mixing ratio of nitrogen of 1˜30% atm, with said carbonlayer being formed according to a plasma CVD method, and lying incontact with the lubricating film.

The thickness of the carbon layer is preferably in the range of 5˜100 Å,while the thickness of the tantalum nitrogen layer is preferably 1˜95 Å.

The method for manufacturing a magnetic recording medium according tothe present invention may comprise the steps of forming (1) anon-magnetic base film and magnetic film on a non-magnetic substrate;(2) a tantalum nitrogen layer thereon, which comprises a materialcontaining nitrogen and tantalum, with a mixing ratio of nitrogen of1˜30% atm; (3) a carbon layer thereon, which is formed according to aplasma CVD method, using a reactant gas containing carbon atoms; and (4)a lubricating film thereon, which lies in contact with the carbon layer.

The aforementioned reactant gas is preferably a mixed gas of hydrocarbonand hydrogen with a mixing ratio of hydrocarbon to hydrogen in the rangeof 2 to 1˜1 to 100 by volume. The hydrocarbon preferably comprises atleast one type of hydrocarbon selected from among lower saturatedhydrocarbons, lower unsaturated hydrocarbons, and lower cyclichydrocarbons.

In addition, the method for manufacturing a magnetic recording mediumaccording to the present invention may comprise a method formanufacturing a magnetic recording medium by means of forming (1) anon-magnetic base film and magnetic film; (2) a carbon film thereon,using a reactant gas containing carbon atoms as a starting material,according to a plasma CVD method; and subsequently (3) a lubricatingfilm on the carbon protective film; wherein the surface of the carbonprotective film is irradiated with ultraviolet rays before forming thelubricating film.

The wavelength of the ultraviolet rays irradiating the carbon protectivefilm is preferably in the range of 100˜400 nm, and the source of theultraviolet rays is preferably an excimer emission lamp.

Additionally, the surface of the carbon protective film is preferablywashed, using water, before forming the lubricating film thereon.

The aforementioned reactant gas preferably comprises a mixed gas ofhydrocarbon and hydrogen, with a mixing ratio of hydrocarbon to hydrogenin the range of 2 to 1˜1 to 100 by volume. The hydrocarbon preferablycomprises at least one type of hydrocarbon selected from among lowersaturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclichydrocarbons.

In addition, the method for manufacturing a magnetic recording mediummay comprise a method for manufacturing a magnetic recording medium bymeans of forming (1) a non-magnetic base film and magnetic film; (2) acarbon film thereon, using a reactant gas containing carbon atoms as astarting material, according to a plasma CVD method; and subsequently(3) a lubricating film on the carbon protective film; wherein thesurface of the carbon protective film is washed, using water, beforeforming the lubricating film thereon.

When washing the carbon protective film, the cleaning water usedpreferably comprises water of a high purity.

In addition, the magnetic recording medium according to the presentinvention may comprise a non-magnetic base film, magnetic film, carbonprotective film, and lubricating film on a non-magnetic substrate,wherein the carbon protective film is formed according to a plasma CVDmethod, followed by irradiation of the surface of the carbon protectivefilm with ultraviolet rays.

Additionally, the magnetic recording medium according to the presentinvention may comprise a non-magnetic base film, magnetic film, carbonprotective film, and lubricating film on a non-magnetic substrate,wherein the carbon protective film is formed, using a reactant gascontaining carbon atoms as a starting material, according to a plasmaCVD method, and the lubricating film principally comprises at least onechemical compound represented by the following formula (1) through (5),the number average molecular weights of which lie in the range of500˜6000.

 F—(CF₂CF₂CF₂O)_(p)—CF₂CF₂—COOCH₂CH_(2—O—C) ₆H₅  (2)

F—(CF₂CF₂CF₂O)_(q)—CF₂CF₂CH₂—OH  (3)

HOCH₂—CF₂O—(C₂F₄O)_(r)—(CF₂O)_(s)—CF₂—CH₂OH  (4)

HO—(CH₂CH₂—O)_(t)—CH₂CF₂O—(CF₂CF₂O)_(u)—(CF₂O)_(v)—CF₂CH₂—(OCH₂CH₂)_(w)—OH  (5)

[wherein, m, n, p, q, r, s, t, u, v, and w each represents an integer].

Additionally, the lubricating film may principally comprise a mixture,which is formed by means of adding a chemical compound represented bythe following formula (6), into the aforementioned chemical compound, ata mixing ratio 0.1˜20% by weight.

[wherein, x represents an integer between 0 and 6].

Among the aforementioned, in particular, a lubricating film principallycomprising a compound represented by the aforementioned formula (1) or(5), the number average molecular weights of which lie in the range of500˜6000, is preferred.

In addition, the aforementioned magnetic recording medium may comprise anon-magnetic base film, a magnetic film containing Co, and a carbonprotective film formed according to a plasma CVD method, on anon-magnetic substrate; wherein the extraction amount of Co is nogreater than 3 ng/cm² with respect to the area of the substrate, andpreferably no greater than 2 ng/cm², and more preferably, no greaterthan 1.5 ng/cm².

In addition, the method for manufacturing a magnetic recording mediumaccording to the present invention may comprise a method formanufacturing a magnetic recording medium by means of forming (1) anon-magnetic base film and magnetic film on a non-magnetic substrate;and (2) a carbon protective film thereon, using a reactant gascontaining carbon atoms as a starting material, according to a plasmaCVD method; wherein the surface of the non-magnetic substrate is treatedwith texture-processing to form an average roughness (Ra) of the surfaceof the non-magnetic substrate is 1˜20 Å.

When texture-processing the surface of the non-magnetic substrate in theaforementioned manner, the average roughness of the surface is morepreferably in the range of 3˜10 Å.

The method for texture-processing is preferably a mechanical method fortexture-processing, in which abrasive particles are used, preferredexamples of which may include processes in which the average particlediameter is 0.1˜0.5 μm.

The method for mechanical texture-processing is a method for treatingthe surface of the non-magnetic substrate with texture-processing, bymeans of rotating the non-magnetic substrate while At the same timerunning an abrasive tape over the substrate in contact with the surfaceof the non-magnetic substrate, and supplying abrasive particles betweenthe abrasive tape and non-magnetic substrate. In this method, it ispreferable to oscillate the abrasive tape in a direction which crossesthe aforementioned running direction, at a frequency of 0.1˜5 Hz.

The rotational speed of the non-magnetic substrate when performingtexture-processing is preferably in the range of 300˜2000 rpm.

The aforementioned reactant gas is preferably a mixed gas of hydrocarbonand hydrogen, wherein the hydrocarbon preferably comprises at least onetype of hydrocarbon selected from among lower saturated hydrocarbons,lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.

In addition, the magnetic recording medium according to the presentinvention may comprise a non-magnetic base film, magnetic film, andcarbon protective film, which are formed on the non-magnetic substrateaccording to a plasma CVD method; wherein the average surface roughness(Ra) of the non-magnetic substrate is in the range of 1˜20 Å.

In addition, the method for manufacturing a magnetic recording mediumaccording to the present invention is a method for manufacturing amagnetic recording medium by means of forming a carbon protective filmon a disc, the non-magnetic substrate of which is layered with anon-magnetic base film and magnetic film, using a reactant gascontaining carbon atoms as a starting material, according to a plasmaCVD method; wherein bias applying is performed to the disc at the timeof forming the carbon protective film, and the reactant gas is eitherbutadiene gas or a mixed gas of butadiene and hydrogen comprising amixing ratio of butadiene to hydrogen in the range of 100 to 0˜1 to 100by volume.

With regard to the aforementioned reactant gas, the mixing ratio ofbutadiene to hydrogen is preferably in the range of 100 to 0˜1 to 25 byvolume.

Additionally, the method for manufacturing a magnetic recording mediumaccording to the present invention may comprise a method formanufacturing a magnetic recording medium by means of exposing a disc,in which both surfaces of the non-magnetic substrate are layered with anon-magnetic base film and magnetic film, to a reactant gas containingcarbon atoms, while supplying electrical power to electrodes arranged onboth sides of the disc to generate plasma, and form a carbon protectivefilm on both sides of the disc, using the aforementioned reactant gas asa starting material, according to a plasma CVD method; wherein biasapplying is performed to the disc at the time of forming the carbonprotective film; the electrical power supplied to the aforementionedelectrodes comprises high frequency electrical power; and the reactantgas comprises either butadiene gas or a mixed gas of butadiene andhydrogen, with a mixing ratio of butadiene to hydrogen in the range of100 to 0˜1 to 100 by volume.

When forming the carbon protective film, it is preferable to make thephases of electrical power supplied to each electrode arranged on bothsides of the disc different from each other. The phase difference in thephase of electrical power supplied to each electrode is preferably inthe range of 90˜270°, and in particular, more preferably comprises theopposite phase (i.e., 180°).

The thickness of the carbon protective film is preferably in the rangeof 30˜100 Å.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural view, showing the plasma CVD apparatus,used in an embodiment of the method for manufacturing a magneticrecording medium according to the present invention.

FIG. 2 is a cross-sectional view, showing an embodiment of the magneticrecording medium according to the present invention.

FIG. 3 is a schematic structural view, showing the main portion of themagnetic recording medium manufacturing apparatus which employs theplasma CVD apparatus shown in FIG. 1.

FIG. 4 is a cross-sectional view, showing an embodiment of the magneticrecording medium according to the present invention.

FIG. 5 is a schematic structural view, showing the spatter equipmentused in an embodiment of the method for manufacturing a magneticrecording medium according to the present invention.

FIG. 6 is a schematic structural view, showing the ultraviolet rayirradiation equipment used in an embodiment of the method formanufacturing a magnetic recording medium according to the presentinvention.

FIG. 7 is a schematic structural view, showing the washing apparatusused in an embodiment of the method for manufacturing a magneticrecording medium according to the present invention.

FIG. 8 is a cross-sectional view, showing an embodiment of the magneticrecording medium according to the present invention.

FIGS. 9(a) and 9(b) are schematic structural views, showing thetexture-processing equipment used in an embodiment of the method formanufacturing a magnetic recording medium according to the presentinvention: FIG. 9(a) shows a front view and FIG. 9(b) shows a side view.

BEST MODES FOR CARRYING OUT THE INVENTION

FIG. 1 shows the plasma CVD apparatus, which serves as the main portionof the manufacturing apparatus used in an embodiment of the method formanufacturing a magnetic recording medium according to the presentinvention. This plasma CVD apparatus is used to form a carbon protectivefilm, and comprises a chamber 10 for storing the disc; electrodes 11 and11 which are arranged in a manner such that they face the inner surfacesof both walls of chamber 10; high frequency electrical power sources 12and 12 which supply high frequency electrical power to theaforementioned electrodes 11 and 11; an electrical bias source 13 whichcan be connected to the disc housed inside of the chamber 10; and asupply source 14 for the reactant gas which serves as a startingmaterial of the carbon protective film formed onto the disc.

The chamber 10 is connected to introduction tubes 15 and 15 which directthe reactant gas supplied from the supply source 14 into the chamber 10,and an exhaust tube 16 which sends gas inside of the chamber 10 out ofthe system. This exhaust tube 16 is provided with an exhaust volumeregulating valve 17, which allows for the appropriate regulation of theinner pressure of the chamber 10.

The high frequency electrical power source 12 is preferably one that cansupply an electrical power of 50˜2000 W to the electrode 11, whenforming the carbon protective film.

Additionally, preferred examples of the electrical bias source 13 mayinclude a high frequency electrical power source and/or a pulse D.C.electrical power source. The high frequency electrical power source canpreferably apply a high frequency electrical power of 10˜300 W to thedisc. Additionally, the pulse D.C. electrical power source canpreferably apply an average voltage of −400˜−10V to the disc.

In the following, an embodiment of the method for manufacturing amagnetic recording medium according to the present invention isdescribed, in which the aforementioned manufacturing equipment is usedas an example.

Initially, a non-magnetic base film and magnetic film are formed on bothsides of a non-magnetic substrate according to a method such as aspatter-coating method or the like, to obtain a disc D.

The non-magnetic substrate may comprise any substrate that is generallyused as a substrate for a magnetic recording medium, examples of whichmay include an aluminium alloy substrate coated with a NiP metal film,and substrates comprising glass, silicone, and the like. The surface ofthe non-magnetic substrate is preferably treated with texture-processingsuch as mechanical texture-processing. In particular, the averagesurface roughness (Ra) is preferably in the range of 1˜20 Å.

Preferred examples of the material for the non-magnetic base filminclude Cr, alloys of Cr and Ti, alloys of Cr and W, alloys of Cr and V,and alloys of Cr and Si.

Preferred examples of the material for the magnetic film include Coalloys such as alloys of Co and Cr; alloys of Co, Cr, and Ta; alloys ofCo, Cr, and Pt; alloys of Co, Cr, Pt, and Ta; and the like.

The thicknesses of the non-magnetic base film and magnetic film arepreferably in the range of 50˜1000 Å, and 50˜800 Å, respectively.

Subsequently, the disc D is transported into a chamber 10 of the plasmaCVD apparatus, and the surface of the disc D is exposed to a reactantgas, which is continuously supplied from a supply source 14 via anintroduction tube 15 into the aforementioned chamber 10, where this gasis removed via an exhaust tube 16 to continuously circulate the gastherein.

The reactant gas is a mixed gas of hydrocarbon and hydrogen, with amixing ratio of hydrocarbon to hydrogen in the range of 2 to 1˜1 to 100by volume.

The hydrocarbon preferably comprises at least one type of hydrocarbonselected from among lower saturated hydrocarbons, lower unsaturatedhydrocarbons, and lower cyclic hydrocarbons.

Examples of the lower saturated hydrocarbon may include methane, ethane,propane, butane, octane, and the like. Furthermore, examples of thelower unsaturated hydrocarbons may include ethylene, propylene,butylene, butadiene, and the like. Additionally, examples of the lowercyclic hydrocarbon may include benzene, toluene, xylene, styrene,naphthalene, cyclohexane, cyclohexadiene, and the like.

Among the aforementioned hydrocarbons, toluene is particularlypreferred, and the mixing ratio of toluene to hydrogen is preferably inthe range of 1 to 15˜1 to 20 by volume.

Hereinafter, a “lower hydrocarbon” signifies a hydrocarbon having 1˜10carbon atoms. In addition, a “cyclic hydrocarbon” represents ahydrocarbon possessing a ring structure such as a benzene ring, and thelike.

The reason for limiting the mixing ratio of hydrocarbon and hydrogen tothe aforementioned range is twofold: a mixing ratio of hydrocarbon tohydrogen falling below the aforementioned range results in a reducedcoating rate, which is unsuitable for practical, industrial production.On the other hand, a mixing ratio exceeding the aforementioned range,results in a high stress remaining within the carbon protective film,which in turn lowers the adhesion strength and CSS resistance of theresultant carbon protective film.

In addition, a lower hydrocarbon is preferably used as thehydrocarbon—if the number of carbon atoms of the hydrocarbon exceeds theaforementioned range, it is difficult to supply the hydrocarbon as agas, and in addition, at the time of discharge, difficulty with thedecomposition of hydrocarbons is encountered, which in turn leads to acarbon protective film containing high polymers that are inferior instrength.

When performing the aforementioned operation, the flow rate of thereactant gas is preferably 50˜500 sccm. In addition, the inner pressureof the chamber 10 is preferably set at a predetermined value such as0.1˜10 Pa, by means of appropriately adjusting the flow rate of theexhaust gas from the chamber 10, using the exhaust regulating valve 17.

At the same time, using the high frequency electrical power source 12,high frequency electrical power of preferably 50˜2000 W is supplied tothe electrodes 11 to generate plasma, and a carbon protective film isformed on both sides of the disc D by means of plasma chemical gas phasegrowth, using the aforementioned reactant gas as a starting material.The thickness of the carbon protective film is preferably in the rangeof 30˜100 Å. The carbon protective film can be formed at the same timeon both sides of the disc D.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode 11 different from each other. By means of making the phases ofelectrical power supplied to each electrode different, the coating rateand durability of the protective film can be improved. The difference inthe phase of electrical power supplied to each electrode is preferablyin the range of 90˜270°, and in particular the opposite phase (i.e.,180°) is preferred.

In addition, when forming the carbon protective film, it is preferableto form a film while performing bias applying, such as high frequencybias or pulse D.C. bias, to the disc D, using the electrical bias source13. When using a high frequency electrical source as the electrical biassource 13, high frequency electrical power of 10˜300 W is preferablyapplied to the disc D. Additionally, when using a pulse D.C. electricalsource as the electrical bias source 13, a voltage of −400˜−10V (at anaverage) is preferably applied to the disc D. Furthermore, the width ofpulse is preferably in the range of 10˜50000 ns, and the frequency ispreferably in the range of 10 kHz˜1 GHz.

When performing bias applying to the disc D, bias applying may beperformed directly to the disc D, or alternatively bias applying may beperformed via a disc carrier (not shown).

In order to accommodate for practical, industrial production, thecoating rate of the carbon protective film is preferably at least 200Å/min, and more preferably at least 400 Å/min.

In addition, a lubricating film may be provided onto the protectivefilm, by means of applying lubricant such as a fomblin lubricant,perfluoropolyether, and the like, according to a dipping method or thelike.

In the following, the effects of the present invention are explained indetail using concrete examples.

TEST EXAMPLES 1˜12

An aluminium substrate coated with a NiP metal film, which had beentreated with texture-processing using an alumina slurry to form anaverage surface roughness of 20 Å, was set into the chamber of a DCMagnetron Spatter Apparatus, and the gas within the chamber wasexhausted to an ultimate vacuum level of 2×10⁻⁶ Torr. Subsequently, abase film comprising Cr with a thickness of 400 Å, and a magnetic filmcomprising an alloy of Co₈₂Cr₁₅Ta₃ (at %) were successively formed onboth sides of the substrate, to obtain a disc D.

Subsequently, the disc D was transported into a chamber 10 of theaforementioned plasma CVD apparatus, and a mixed gas of hydrocarbon andhydrogen comprising a mixing ratio shown in Table 1 was supplied intothe chamber as a reactant gas. The inner pressure of the chamber 10 wasmaintained at 2 Pa.

At the same time, high frequency electrical power (of 13.56 MHz) of 300W was supplied to the electrodes 11 to generate plasma while a highfrequency bias of 50 W, under the conditions shown in Table 1, wasapplied to the disc D, to form a carbon protective film with a thicknessof 50 Å on both sides of the disc D. The temperature of the disc Dduring coating was maintained at 130° C. (In Test Example 9, theelectrical power supplied to the electrode 11 was 600 W, and thetemperature of the disc during coating was 136° C. Furthermore, the biasused in Test Example 3 comprised a D.C. bias of −200V). The distancebetween the disc D and electrode 11 was set at 30 mm. Furthermore, inthe table, the “RF phase difference” signifies the difference in thephase of electrical power supplied to the two electrodes 11 and 11.

TABLE 1 Mixing Bias RF Coating Gas ratio frequency differ- rate type(sccm) (kHz) ence (°) (Å/min) Note Test Toluene  10:150 400 180 335Example 1 Test Toluene  10:120 400 0 202 Example 2 Test Toluene  10:120D.C. bias 180 188 −200 V Example 3 Test Toluene  10:120 400 180 460Example 4 Test Toluene  15:120 400 180 1098 Example 5 Test Toluene100:50  400 180 1181 Example 6 Test Toluene 100:0  400 180 2344 Example7 Test Meth- 100:0  400 180 324 Example 8 ane Test Meth- 60:60 no bias 0161 Example 9 ane Test Ethane 100:0  400 180 385 Example 10 Test Acetone100:0 400 180 221 Example 11 Test Toluene 10:150 no bias 180 290 Example12 *Mixing ratio: the ratio of the gas shown in the “Gas Type” column toH₂

Table 1 shows the coating rates of each carbon film. Comparing TestExamples 4 through 7, it is clear that increasing the mixing ratio oftoluene results in an increased coating rate. However, in Test Examples6 and 7, the coating rate did not improve relative to the mixing ratioof toluene. This result is assumed secondary to the diffusion of plasmafrom sparks incurred during discharge. In addition, when comparing TestExamples 1˜5 and 12, it is clear that the improvements in the coatingrate can be achieved by means of bias applying, in particular the highfrequency bias applying, and/or making the phases of the electricalpower supplied to electrodes which are at front and reverse sides of thedisc different from each other.

Subsequently, a fomblin lubricant was applied to the carbon protectivefilm at 15 Å, to obtain a magnetic recording medium.

The resultant magnetic recording medium was used in the CSS test, asdescribed in the following. In this test, a CSS operation was performed20000 times using an MR head, wherein once cycle consisted of buildingup for five seconds; high speed rotation for one second; trailing downfor five seconds; and parking for one second, at a rotational speed of7200 rpm, under the conditions of ambient temperature and normalhumidity.

Furthermore, with regard to Test Examples 3˜5, a stiction value wasmonitored, and another CSS test was performed in which a CSS operationwas carried out 5000 times, using the same cycle as described above, ata temperature of 40° C. with a humidity of 80%. The results are shown inTable 2. When a crash occurred during the CSS test performed under anormal temperature and pressure, the number of CSS cycles at the timewhen the crash occurred was recorded.

In Table 2, the ratio of the g-band peak value (vG-line) and d-band peakvalue (Id/Ig) according to Raman spectral analysis (argon ion laserexcitation) is also shown for reference. In general, when a carbon filmis analyzed according to the Raman spectral analysis, a profile with twopeaks is obtained in which a g-band is measured at approximately 1530cm⁻¹ and a d-band is measured at approximately 1400 cm⁻¹. A smallervalue for Id/Ig, or alternatively, a higher frequency for the g-bandpeak results in greater diamond-like characteristics in the carbon film.

Subsequently, the same magnetic recording medium used in the CSS testwas used in a corrosion test, as described in the following. This testcomprised the steps of leaving the test medium in an oven at atemperature of 60° C. with a humidity of 80% for 96 hours; subsequentlysoaking the medium in 50 cc of pure water for 30 minutes; and measuringthe amount of Co extracted in the pure water. In addition, another test,was performed in the same manner as described above, with the exceptionthat the aforementioned magnetic recording medium was allowed to sit ata normal temperature (25° C.) and humidity (50%) for 96 hours. Theresults are shown in Table 2.

Furthermore, in the present specification, the term “crash” signifiesthe occurrence of a head crash during the CSS test, while the phrase “nocrash” signifies that such a head crash did not occur.

TABLE 2 CSS Test Normal Co Corrosion Test Raman Analysis temp & Normal60° C., 80% vG-line pressure 40° C., 80% Stiction (μg/disc) (μg/disc)(cm⁻¹) Id/Ig Test Example 1 8500 — — 0.07 0.17 1543.2 0.56 Test Example2 5000 — — 0.08 0.18 1550.2 0.66 Test Example 3 No crash 5000 0.44 0.060.14 1559.2 1.56 Test Example 4 No crash 5000 0.38 0.05 0.07 1553.0 0.63Test Example 5 No crash 5000 0.34 0.08 0.12 1524.5 0.39 Test Example 67000 — — 0.18 0.28 1547.2 0.78 Test Example 7 250 — — 0.22 0.54 — — TestExample 8 10 — — 0.11 0.18 — — Test Example 9 4000 — — 0.09 0.19 1534.00.45 Test Example 10 10 — — 0.14 0.22 — — Test Example 11 10 — — 0.130.77 — — Test Example 12 20 — — 0.18 0.25 — —

From Table 2, it is clear that with the magnetic recording mediummanufactured according to Test Examples 1 through 6, the above describedcrashes did not occur, even when the CSS operation was performed greaterthan 5000 times. In particular, Test Examples 3˜5, did not result incrashes even when the CSS operation was performed 20000 times, and alsodid not result in crashes when the CSS operation was performed 5000times, under the conditions of a temperature of 40° C. and a humidity of80%, and thus these examples exhibited a favorable performance withregard to resistance to CSS.

On the other hand, Test Example 7, in which the mixing ratio of tolueneand H₂ was out of the range defined in the present invention, and TestExample 12, in which bias applying was not performed, resulted in amodest coating rate, but a magnetic recording medium of inferiordurability.

Additionally, the magnetic recording medium obtained according TestExamples 8˜11, in which methane, ethane, or acetone was employed, allexhibited an inferior durability.

In addition, the results of the corrosion test confirmed that theextraction amount of Co of all magnetic recording media wasapproximately 1˜2 ng per medium, leaving no problems with respect topractical use.

Furthermore, the results of the CSS test showed clearly that it ispossible to improve the durability of the resultant magnetic recordingmedium, by means of making the phases of electrical power supplied tothe electrodes on each side of the disc different.

In addition, according to the results of Test Examples 1˜6, it ispossible to form a carbon protective film at a coating rate suitable forindustrial production, and to provide a magnetic recording mediaexhibiting superior performance with respect to their resistance to CSSand resistance to corrosion.

As described in the aforementioned, according to the present invention,it is possible to efficiently form a carbon protective film possessing asuperior durability. Accordingly, it is possible to make the carbonprotective film thinner while maintaining a sufficient durability,thereby reducing the spacing loss.

Thus, it is possible to efficiently provide a reliable, magneticrecording medium, which can support a sufficiently high recordingdensity without reduction in its output properties.

In the following, another embodiment of the method for manufacturing amagnetic recording medium according to the present invention isdescribed, using an example in which the plasma CVD apparatus shown inFIG. 1 is employed.

Initially, a non-magnetic base film and magnetic film are formed on bothsides of the non-magnetic substrate according to a method such as aspatter-coating method or the like, to obtain a disc D.

The non-magnetic substrate can comprise any substrate that is generallyused as a substrate for a magnetic recording medium, as described in theaforementioned. The material and thickness of the non-magnetic base filmand magnetic film are also as described aforementioned.

Subsequently, the disc D, layered with a non-magnetic base film andmagnetic film on the non-magnetic substrate according to theaforementioned operations, is transported into chamber 10 of theaforementioned plasma CVD apparatus, and the surface of the disc D isexposed to the reactant gas, which is continuously supplied from asupply source 14 via an introduction tube 15 into the chamber 10, wherethe gas is exhausted via an exhaust tube 16 to circulate the gastherein.

The reactant gas is preferably a mixed gas comprising hydrocarbon andhydrogen, with a mixing ratio of hydrocarbon to hydrogen in the range of2 to 1˜1 to 100 by volume, as described in the aforementioned. Thehydrocarbon preferably comprises at least one type of hydrocarbonselected from among lower saturated hydrocarbons, lower unsaturatedhydrocarbons, and lower cyclic hydrocarbons.

When carrying out this operation, the flow rate of the reactant gas ispreferably 50˜500 sccm. Additionally, the inner pressure of the chamber10 is preferably set at a predetermined value, such as 0.1˜10 Pa.

At the same time, using the high frequency electrical power source 12, ahigh frequency electrical power of preferably 50˜2000 W is supplied tothe electrodes 11 to generate plasma, and a carbon protective film isformed on both sides of the disc D by means of the plasma chemical gasphase growth, using the aforementioned reactant gas as a startingmaterial. The thickness of the carbon protective film is preferably inthe range of 30˜100 Å.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode 11 different. By means of making the phases of electricalpower supplied to each electrode different, the coating rate anddurability of the protective film can be improved. The difference in thephase of electrical power supplied to each electrode is preferably inthe range of 90˜270°, with a particular preference for the oppositephase (i.e., 180°).

According to this embodiment of the method for manufacturing a magneticrecording medium, when forming a carbon protective film, it ispreferable to form the film while applying pulse D.C. bias having afrequency of 1 kHz˜100 GHz (with a cycle of 10 ns˜1 ms) and pulse widthof 1 ns˜500 μs, to the disc D, using an electrical bias source 13.

A pulse D.C. bias frequency of less than 1 kHz or exceeding 100 GHz,results in a carbon protective film of inferior durability. Inparticular, when the frequency is less than 1 kHz, the coating ratetends to be lower, leading to an unfavorable reduction in the productionefficiency.

The frequency and pulse width of the aforementioned pulse D.C. bias ispreferably 10 kHz˜1 GHz, and 10 ns˜50 μs, respectively.

Furthermore, the average voltage of the pulse D.C. bias applied to thedisc is preferably −400˜−10V.

When the average voltage is less than −400V, sparks are likely to begenerated during the coating, leading to a high likelihood of generatingabnormal growth portions on the surface of the carbon protective film.When the average voltage exceeds −10V, the carbon protective film tendsto contain a greater number of high polymers, which are inferior instrength.

In addition, a lubricating film may be provided on the protective filmby means of applying the aforementioned lubricant.

Examples of the magnetic recording medium manufactured according to theaforementioned manufacturing method may include a magnetic recordingmedium with the structure shown in FIG. 2.

In the magnetic recording medium according to this embodiment, anon-magnetic substrate S, a non-magnetic base film 31, a magnetic film32, a carbon protective film 33, and a lubricating film 34 are provided.

According to the aforementioned manufacturing method, at the time offorming the carbon protective film, it is possible to efficiently form acarbon protective film displaying a superior durability, since pulseD.C. bias with a frequency of 1 kHz˜100 GHz and pulse width of 1 ns˜500μs is applied to the disc. Accordingly, it is possible to make thecarbon protective film thinner while also maintaining durability, andthus provide a magnetic recording medium that is capable of reducingspacing loss. In addition, it is possible to increase the coating rate,and production efficiency therein.

Therefore, it is possible to efficiently provide a reliable, magneticrecording medium, which can support a sufficiently high recordingdensity without lowering the output properties thereof.

In the following, the effects of the present invention are specified,using concrete examples.

TEST EXAMPLES 13˜26

After an aluminium alloy substrate coated with a NiP metal film (with adiameter of 95 mm and thickness of 0.8 mm) was treated with mechanicaltexture-processing to form an average surface roughness of 20 Å, anon-magnetic base film (with a thickness of 600 Å) comprising a Cralloy, and a magnetic film comprising a Co alloy were successivelyformed on both sides of the substrate, using spattering device (3010manufactured by Anelva) to obtain a disc D.

Subsequently, the disc D was transported into a chamber 10 of theaforementioned plasma CVD apparatus, and a mixed gas was supplied fromthe supply source 14 into the chamber to achieve a flow rate of 130sccm.

A mixed gas of toluene and hydrogen, with a mixing ratio of toluene tohydrogen of 1 to 12 by volume, was used as the reactant gas.Additionally, the inner pressure of the chamber 10 was maintained at 6Pa.

At the same time, pulse D.C. bias was applied to the disc under theconditions shown in Table 3, using an electrical bias source 13, andhigh frequency electrical power of 300 W, or alternatively 500 W, wassupplied to the electrodes 11 to generate plasma and form a carbonprotective film with a thickness of 50 Å on both sides of the disc D.

The temperature of the disc D during coating was maintained at 130° C.The difference in the phase of high frequency electrical power suppliedto each electrode 11 was set at 180°. In addition, the distance betweenthe disc D and electrode 11 was set at 30 mm.

Subsequently, a magnetic recording medium was obtained by means ofapplying a fomblin lubricant (Fomblin Zdol 2000) to the carbonprotective film, according to a dipping method, to form a lubricatingfilm thereon with a thickness of 20 Å.

The CSS test described in the following was performed on the resultantmagnetic recording media. In the test, using a MR head, a CSS operationwas performed on the magnetic recording medium 10,000 times, at arotational speed of 7200 rpm, and a temperature of 40° C. with ahumidity of 80%. After allowing the magnetic recording medium to sit for1 hour, the dynamic stiction value was monitored. The results are shownin Table 3.

In the table, the term “plasma RF electrical power” represents theelectrical power supplied to the electrodes 11 during the formation ofthe carbon protective film.

TABLE 3 Bias Plasma RF Coating Bias Pulse voltage electrical rateStiction frequency width (V) power (W) (Å/min) (−) Test Example 13 1 kHz500 ns −120 500 405 0.81 Test Example 14 200 kHz 500 ns −120 500 7530.40 Test Example 15 2 MHz 250 ns −120 300 712 0.55 Test Example 16 10MHz 50 ns −120 500 844 0.46 Test Example 17 200 kHz 1 ns −120 500 4770.88 Test Example 18 200 kHz 1000 ns −120 500 777 0.44 Test Example 19 1kHz 500000 ns −120 500 624 0.67 Test Example 20 70 GHz 50 ns −100 500553 0.66 Test Example 21 101 GHz 1 ns −100 500 413 Crash Test Example 220.5 kHz 500 ns −100 500 388 Crash Test Example 23 200 kHz 500 ns −400500 1042 Crash Test Example 24 200 kHz 0.5 ns −100 500 340 Crash TestExample 25 1 kHz 0.8 ms −100 500 314 Crash Test Example 26 — — — 300 335Crash

From the results of the CSS test shown in Table 3, it is clear that themagnetic recording media obtained according to the method for applyingpulse D.C. bias with a frequency of 1 kHz˜100 GHz and pulse width of1ns˜500 μs to the disc, at the time of forming the carbon protectivefilm, were superior in durability and exhibited a higher coating rate.

As described in the aforementioned, according to the present invention,it is possible to efficiently form a carbon protective film with asuperior durability. Accordingly, it is possible to make the carbonprotective film thinner while also maintaining a sufficient durability,and thereby reduce spacing loss.

Therefore, it is possible to provide a highly reliable, magneticrecording medium, which can support a sufficiently high recordingdensity without lowering the output properties.

FIG. 3 shows the manufacturing equipment used in another embodiment ofthe method for manufacturing a magnetic recording medium according tothe present invention. The manufacturing equipment shown herein isprovided with a spattering device 1, temperature regulating device 2,and plasma CVD apparatus 3.

The spattering device 1 is used to form a non-magnetic base film,magnetic film, and the like, on a non-magnetic substrate, and maycomprise any apparatus generally used for manufacturing a magneticrecording medium.

The temperature regulating device 2 sets the temperature of the discsent to the aforementioned plasma CVD apparatus 3 to a predetermineddegree, and comprises a chamber 4, which stores the disc, and a supplysource for supplying the temperature adjusting gas 5, which is used foradjusting the temperature of the disc in the chamber 4. Theaforementioned chamber 4 is connected to an introduction tube 7, whichdirects the temperature adjusting gas supplied from the supply source 5into the chamber 4, and an exhaust tube 8, which expels the gas insidethe chamber 4 out of the system.

The aforementioned chamber 4 comprises an airtight structure, and isprovided with a transport entrance 4 a, which transports a disc passingthrough the spattering device 1 into the chamber 4, and a transport exit4 b, which transports the disc out of the chamber 4 towards theaforementioned plasma CVD apparatus 3.

The aforementioned plasma CVD apparatus 3 may comprise the samestructure shown in FIG. 1.

In the following, another embodiment of the method for manufacturing amagnetic recording medium according to the present invention isdescribed, using an example in which the aforementioned manufacturingequipment is employed.

Initially, using a spattering device 1, a non-magnetic base film andmagnetic film are formed on both sides of the non-magnetic substrate, toobtain a disc D.

The non-magnetic substrate may comprise any substrate that is generallyused as a substrate for a magnetic recording medium, as described in theaforementioned. The material and thickness of the non-magnetic base filmand magnetic film are similarly as described in the aforementioned.

In general, when forming the non-magnetic base film and magnetic film,the temperature of the non-magnetic substrate is approximately 250˜350°C.

Subsequently, the disc D, layered with the non-magnetic base film andmagnetic film on the non-magnetic substrate according to theaforementioned operations, is transported into the chamber 4 of thetemperature regulating device 2 through the transport entrance 4 a, andthe disc D in the chamber 4 is exposed to the temperature adjusting gas,which is supplied from the supply source 5 via the introduction tube 7into the chamber 4, from which the gas is exhausted via the exhaust tube8 to circulate the gas within.

The temperature adjusting gas is not particularly limited, as long as itdoes not adversely affect the disc D; examples of the aforementioned gasmay include hydrogen, nitrogen, helium, neon, argon, and the like.

The temperature of the temperature adjusting gas is appropriatelydetermined according to the desired temperature of the disc D, and otherconditions, such as a flow rate of the temperature adjusting gas and thelike; however, this temperature is preferably in the range of 0˜250° C.

When carrying out this operation, the flow rate of the temperatureadjusting gas is preferably 50˜1500 sccm. Additionally, the innerpressure of the chamber 4 is preferably set at a predetermined value,e.g., 1˜30 Pa by means of appropriately adjusting the flow rate of theexhaust gas from the chamber 4.

By means of exposing the disc D to the temperature adjusting gas, heatexchange is performed between the disc D and temperature adjusting gas.This operation is continued until the temperature of the disc D is inthe range of 100˜250° C., preferably 150˜250° C., and more preferably150˜200° C.

If the temperature of the disc D is less than 100° C., the density ofthe carbon protective film formed onto the disc D, according to theoperation described in the following, results in a low value, whichleads to an inferior durability.

If the temperature exceeds 250° C., the kinetic energy of the moleculesof the reactant gas becomes too high during the formation of the carbonprotective film according to the operation described in the following,which in turn results in difficulty in adhering the molecules to thedisc D, thereby leading to a low coating rate. In addition, theresultant carbon protective film contains a greater number of highpolymer components that are inferior in strength, which then lead to aninferior durability.

Subsequently, the disc D is transported out of the temperatureregulating device 2 via the transport exit 4 b, and immediately intochamber 10 of the aforementioned plasma CVD apparatus 3, where thesurface of the disc D, the temperature of which has been adjusted to theaforementioned value by means of the temperature regulating device 2, isexposed to a reactant gas, which is supplied from the supply source 14via the introduction tube 15 into the chamber 10. Gas is continuouslyexhausted through the exhaust tube 16 to circulate the gas withinchamber 10.

The reactant gas is preferably a mixed gas of hydrocarbon and hydrogenwith a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1˜1to 100 by volume as described in the aforementioned, and the hydrocarbonpreferably comprises at least one type of hydrocarbon selected fromamong lower saturated hydrocarbons, lower unsaturated hydrocarbons, andlower cyclic hydrocarbons.

When carrying out the operation, the flow rate of the reactant gas ispreferably in the range of 50˜500 sccm. In addition, the inner pressureof the chamber 10 is preferably set at a predetermined value, e.g.,0.1˜10 Pa by means of appropriately adjusting the flow rate of theexhaust gas from the chamber 10, using the exhaust regulating valve 17.

At the same time, using the high frequency electrical power source 12,high frequency electrical power of preferably 50˜2000 W is supplied tothe electrodes 11 to generate plasma and form the carbon protective filmon both sides of the disc D by means of plasma chemical gas phasegrowth, using the aforementioned reactant gas as a starting material.The thickness of the carbon protective film is preferably in the rangeof 30˜100 Å.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode different. By means of making the phases of electrical powersupplied to each electrode 11 different, it is possible to improve thecoating rate and durability of the protective film. The difference inthe phase of electrical power supplied to each electrode is preferablyin the range of 90˜270°, and in particular, more preferably comprisesthe opposite phase (i.e., 180°).

Herein, it is preferable to form the film while performing bias applyingsuch as high frequency bias and pulse D.C. bias to the disc, using theelectrical bias source 13.

The conditions of bias, such as voltage and the like, are preferably asdescribed in the aforementioned.

In addition, a lubricating film may be provided on the protective filmby means of applying a lubricant such as fomblin lubricant,perfluoropolyether, and the like, according to a dipping method or thelike.

In the aforementioned manufacturing method, since the disc temperatureis set at 100˜250° C. in advance, during formation of the carbonprotective film, the carbon protective film is able to support a higherdensity, which leads to a superior durability. Accordingly, it ispossible to make the carbon protective film thinner, while alsomaintaining a sufficient durability, and thus provide a magneticrecording medium that is capable of reducing spacing loss at the time ofrecording and replay.

Therefore, it is possible to provide a highly reliable, magneticrecording medium, which can support a sufficiently high recordingdensity without lowering the output properties thereof.

In addition, it is possible to accelerate adhesion of the materials ofthe carbon protective film, derived from the reactant gas, to the discD, and thereby increase the coating rate and production efficiency.

The reason for the improvement in durability of the carbon protectivefilm by means of setting the temperature of the disc D in theaforementioned range at the time of forming the aforementioned carbonprotective film is unclear; however, the following is hypothesized.

Namely, if the temperature is less than the aforementioned range, thekinetic energy of the molecules of the materials of the carbonprotective film at the time of forming the carbon protective film islow, which results in an insufficient tightness and irregularconfiguration of the carbon protective film molecules. Accordingly, theresultant carbon protective film comprises a lower density, leading toan inferior durability of the carbon protective film.

In addition, if the temperature exceeds the aforementioned range, highpolymer reactions such as polymerization, condensation, and the like aremore likely to occur, and the carbon compounds, derived from thesupplied reactant gas, will tend to form high polymers on the surface ofthe disc D. As a result, the number of high polymer components in thecarbon protective film, which exhibit an inferior strength, increases,thereby leading to an inferior durability in the carbon protective film.

In the following the effects of the present invention are specified,using concrete examples.

TEST EXAMPLES 27˜32

Magnetic recording medium was manufactured as described in thefollowing, using the equipment shown in FIGS. 1 and 3.

After an aluminium alloy substrate coated with a NiP metal film (with adiameter of 95 mm and thickness of 0.8 mm) was treated with mechanicaltexture-processing to form an average surface roughness of 20 Å, anon-magnetic base film (with a thickness of 600 Å) comprising a Cralloy, and a magnetic film comprising a Co alloy were successivelyformed on both sides of the substrate, using a spattering device (3010manufactured by Anelva), to obtain a disc D. At the time of forming theaforementioned non-magnetic base film and magnetic film, the temperatureof the substrate was set at 250° C.

Subsequently, the disc D was transported into the chamber 4 of thetemperature regulating device 2, where hydrogen gas (the temperature ofwhich was adjusted in advance to 20° C.) for use in adjusting thetemperature of the disc was supplied at a flow rate shown in Table 4. Inthis manner, the temperature of the disc D was adjusted to the valuesshown in Table 4 by means of exposing the disc D to the hydrogen gas fora period of time shown in Table 4. Furthermore, the temperature of thedisc D was measured by means of a radiation thermometer provided inchamber 4. The inner pressure of the chamber 4 was set at 10 Pa.

Subsequently, the disc D was immediately transported into the chamber 10of the plasma CVD apparatus 3, and a reactant gas was supplied from thesupply source 14 into the chamber 10 at a flow rate of 130 sccm. A mixedgas of toluene and hydrogen, with a mixing ratio of toluene to hydrogenof 1 to 10 by volume, was used as the reactant gas. In addition, theinner pressure of the chamber 10 was set at 6 Pa.

At the same time, high frequency electrical power of 500 W was suppliedto the electrodes 11 to generate plasma and form a carbon protectivefilm with a thickness of 50 Å on both sides of the disc D. Thetemperature of the disc D was set as shown in Table 4, by means of theaforementioned temperature regulating device 2. In addition, highfrequency electrical power of 50 W was applied to the disc D, using theelectrical bias source 13. In addition, the difference in the phase ofhigh frequency electrical power supplied to each electrode 11 was set at180°.

Subsequently, fomblin lubricant was applied to the carbon protectivefilm, to form a lubricating film with a thickness of 15 Å, and yieldinga magnetic recording medium.

The CSS test described in the following was performed on the resultantmagnetic recording media. In the CSS test, using MR head, a CSSoperation was performed 20,000 times at a rotational speed of 7200 rpm,and a temperature of 40° C. with a humidity of 80%. The dynamic stictionvalue was monitored after allowing the magnetic recording medium to sitfor one hour. The results are shown in Table 4.

TEST EXAMPLES 33˜36

The magnetic recording medium was manufactured in the same manner as inthe aforementioned test examples, with the exception that thetemperature of the disc D, at the time of forming the carbon protectivefilm, was adjusted by means of changing the temperature of the disc D atthe time of transport into the temperature regulating device 2, and/orthe flow rate or temperature of the temperature adjusting gas in thetemperature adjusting operation, using the temperature regulating device2. The test results are also shown in Table 4.

TABLE 4 Flow rate Disc temp. Temp of temp. when Coating regulatingadjusting forming rate Stiction time (sec) gas (sccm) film (° C.)(Å/min) (−) Test Example 27 8 80 238 617 0.72 Test Example 28 13 80 220660 0.66 Test Example 29 20 80 174 765 0.67 Test Example 30 8 200 191720 0.63 Test Example 31 13 200 150 830 0.73 Test Example 32 6 80 250506 0.68 Test Example 33 0 0 327 339 2.59 Test Example 34 2 80 304 3811.48 Test Example 35 13 2000 50 1850 Crash Test Example 36 0 0 400 225Crash

From the results shown in Table 4, it is clear that the magneticrecording media manufactured according to a method in which thetemperature of the disc D was set in the range of 100˜250° C., at thetime of forming the carbon protective film, exhibited a lower stictionvalue after performing the CSS test and a superior durability, inaddition to a higher coating rate, when compared to the magneticrecording media manufactured according to a method in which thetemperature of the disc D was set outside of the aforementioned range.

As described in the aforementioned, in the method for manufacturing amagnetic recording medium according to the present invention, it ispossible to provide a carbon protective film comprising a high densityand superior durability. Accordingly, it is possible to manufacture athinner carbon protective film while also maintaining a sufficientdurability, and thus to provide a magnetic recording medium that iscapable of reducing spacing loss at the time of recording and replay.

Therefore, it is possible to provide a highly reliable magneticrecording medium, which can support a sufficiently high recordingdensity without lowering the output properties thereof. Additionally, itis possible to also increase the production efficiency.

In the following, another embodiment of the method for manufacturing amagnetic recording medium according to the present invention isdescribed, using an example which employs the aforementioned plasma CVDapparatus shown in FIG. 1.

Initially, a non-magnetic base film and magnetic film were formed onboth sides of non-magnetic substrate, according to a method such as aspatter-coating method, and the like, to obtain a disc D.

The non-magnetic substrate may comprise any substrate that is generallyused as a substrate for a magnetic recording medium, as described in theaforementioned. The material and thickness of the non-magnetic base filmand magnetic film are also as described in the aforementioned.

Subsequently, the disc D is transported into the chamber 10 of theaforementioned plasma CVD apparatus, and the surface of the disc D isexposed to the reactant gas, which is supplied from the supply source 14via the introduction tube 15 into the chamber 10, from which the gas isexhausted through the exhaust tube 16 to circulate the gas within.

The reactant gas comprises a mixed gas of hydrocarbon and hydrogen, witha mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1˜1 to100 by volume. The hydrocarbon preferably comprises at least one type ofhydrocarbon selected from among lower saturated hydrocarbons, lowerunsaturated hydrocarbons, and lower cyclic hydrocarbons.

When carrying out this operation, the flow rate of the reactant gas ispreferably in the range of 50˜500 sccm.

According to the method of this embodiment, the flow rate of the exhaustgas from the chamber 10 is appropriately adjusted, using the exhaustregulating valve 17 provided in the exhaust tube 16, such that thepressure of the reactant gas in the chamber 10 falls into the range of0.1˜10 Pa, preferably 2˜6 Pa, and more preferably 4.5˜6 Pa.

The reason for setting the pressure in the aforementioned range is thatthe coating rate decreases if the pressure is less than 0.1 Pa, whilethe durability of the carbon protective film deteriorates if thepressure exceeds 10 Pa.

At the same time, high frequency electrical power of preferably 50˜2000W is supplied to the electrodes 11, using a high frequency electricalpower source 12, to generate plasma, and thereby form a carbonprotective film formed on both sides of the disc D by means of theplasma chemical gas phase growth, using the aforementioned reactant gasas a starting material. The thickness of the carbon protective film ispreferably in the range of 30˜100 Å.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode 11 different. By means of shifting the phase of electricalpower supplied to each electrode, the coating rate and durability of theprotective film can be improved. The difference in the phase ofelectrical power supplied to each electrode is preferably in the rangeof 90˜270°, and in particular the opposite phase (i.e., 180°) ispreferred.

In addition, when forming the carbon protective film, it is preferableto form the film while performing bias applying, such as high frequencybias or pulse D.C. bias, to the disc D, using an electrical bias source13.

The preferred conditions of bias, e.g., voltage and the like are asdescribed in the aforementioned.

In addition, a lubricating film may be provided on the protective filmby means of applying the aforementioned lubricant.

In the aforementioned manufacturing method, since the pressure of thereactant gas is maintained at 0.1˜10 Pa, at the time of forming thecarbon protective film, the resultant carbon protective film exhibits asuperior durability. Accordingly, it is possible to make the carbonprotective film thinner while also maintaining a sufficient durability,and thus provide a magnetic recording medium that is capable of reducingspacing loss at the time of recording and replay.

Thus, it is possible to provide a highly reliable magnetic recordingmedium, which can support a sufficiently high recording density withoutlowering the output properties thereof.

In addition, it is possible to increase the coating rate and productionefficiency.

The reason that a carbon protective film with superior durability can beefficiently formed by means of setting the pressure of the reactant gasin the aforementioned range at the time of forming the aforementionedcarbon protective film is hypothesized in the following.

Setting the pressure for the reactant gas in the aforementioned rangeresults in the excitation and activation of a portion of thehydrocarbons in the reactant gas by the plasma. After decomposition ofthe potion of the hydrocarbons, this portion of hydrocarbons arerestructured onto disc D to form a diamond-like carbon (referred tohereinafter as “DLC”) with high hardness. Thus, the resultant carbonprotective film exhibits superior strength.

In addition, a sufficient reactant gas is thus supplied to the chamber10, leading to a high coating rate.

On the other hand, if the pressure of the reactant gas is less than theaforementioned range, the number of hydrocarbon molecules in thereactant gas which exist in the chamber 10 becomes insufficient, leadingto an inadequate coating rate.

In addition, if the pressure exceeds the aforementioned range, thenumber of hydrocarbon molecules in the reactant gas present withinchamber 10 becomes too high, which in turn leads to difficulty indecomposing the hydrocarbons even in the presence of the plasma. As aresult, a portion of the hydrocarbons in the reactant gas remain adheredto the disc D without undergoing decomposition, and the overall contentof DLC in the resultant carbon protective film decreases, leading to acarbon protective film with an inferior strength.

In the following, the effects of the present invention are specified,using concrete examples.

TEST EXAMPLES 37˜43

After an aluminium alloy substrate coated with a NiP metal film (with adiameter of 95 mm and thickness of 0.8 mm) was treated with mechanicaltexture-processing to form an average surface roughness of 23 Å, anon-magnetic base film (with a thickness of 600 Å) comprising a Cralloy, and a magnetic film comprising a Co alloy were successivelyformed on both sides of the substrate, using a spattering device (3010manufactured by Anelva), to obtain a disc D.

Subsequently, the disc D was transported into the chamber 10 of theaforementioned plasma CVD apparatus, and a mixed gas was supplied fromthe supply source 14 into the chamber to achieve a flow rate of 130sccm. A mixed gas of toluene and hydrogen, with a mixing ratio oftoluene to hydrogen of 1 to 10 by volume, was used as the reactant gas.

The inner pressure of the chamber 10 at this time was maintained asshown in Table 5, by means of adjusting the exhaust regulating valve 17.

At the same time, high frequency electrical power of 500 W was suppliedto the electrodes 11 to generate plasma, and thereby form a carbonprotective film with a thickness of 50 Å on both sides of the disc D. Inaddition, high frequency electrical power of 50 W was applied to thedisc D, using the electrical bias source 13. In addition, the differencein the phase of high frequency electrical power supplied to eachelectrode 11 was set at 180°.

Subsequently, fomblin lubricant was applied to the carbon protectivefilm, to form a lubricating film with a thickness of 15 Å, therebyyielding a magnetic recording medium.

The CSS test described in the following was performed on the magneticrecording media. In the CSS test, using an head, a CSS operation wasperformed 20,000 times at a rotational speed of 7200 rpm, and atemperature of 40° C. with a humidity of 80%. The dynamic stiction valuewas monitored after allowing the magnetic recording medium to sit forone hour. The results are shown in Table 5.

Additionally, Raman spectral analysis (argon ion laser excitation) wasperformed on the aforementioned magnetic recording media, using a Ramanspectral analysis apparatus (manufactured by JEOL Co., Inc). Theseresults are also shown in Table 5.

In general, when a carbon film is analyzed according to the Ramanspectral analysis, a profile with two peaks is obtained in which ag-band is measured at approximately 1530 cm⁻¹ and a d-band is measuredat approximately 1400 cm⁻¹. A smaller value for Id/Ig, or alternatively,a higher frequency for the g-band peak results in greater diamond-likecharacteristics in the carbon film.

TEST EXAMPLES 44 AND 45

A magnetic recording medium was manufactured in the same manner as theaforementioned test example, with the exception that the pressure of thereactant gas in the chamber 10 was modified by means of adjusting theexhaust regulating valve 17. The test results are shown in Table 5.

Additionally, Raman spectral analysis was performed on these magneticrecording media. The results also displayed in Table 5.

TABLE 5 Pressure of Results of Raman reactant Stiction spectral analysisgas (Pa) (−) G-line (cm⁻¹) Id/Ig (−) Test Example 37 2.30 0.71 1540.90.62 Test Example 38 3.60 0.50 1539.9 0.56 Test Example 39 4.70 0.431553.0 0.63 Test Example 40 5.30 0.49 1545.2 0.53 Test Example 41 5.800.46 1547.5 0.66 Test Example 42 6.40 0.83 1535.6 0.51 Test Example 430.88 0.77 1558.9 0.76 Test Example 44 13.1 1.24 1565.5 3.77 Test Example45 16.4 Crash 1566.0 3.89

From the results shown in Table 5, it is clear that the magneticrecording media, manufactured according to a method in which thepressure of the reactant gas at the time of forming the carbonprotective film is maintained at 0.1˜1.0 Pa, are superior in durabilitywhen compared to magnetic recording media manufactured according to amethod wherein the pressure is set outside of the aforementioned range.

Moreover, among the aforementioned, it is clear that magnetic recordingmedia manufactured according to a method in which the pressure of thereactant gas is maintained at 2˜6 Pa, in particular, exhibit a superiordurability.

In addition, the carbon protective films of magnetic recording media,manufactured according to a method wherein the pressure of the reactantgas is maintained in the aforementioned range, display g-band peakvalues at higher frequency when compared to those manufactured accordingto a method wherein the pressure is set outside of the aforementionedrange, which in turn lead to a low Id/Ig and greater DLC content.

As described in the aforementioned, in the method for manufacturing amagnetic recording medium according to the present invention, a carbonprotective film exhibiting a superior durability is produced by means ofmaintaining the pressure of the reactant gas at 0.1˜10 Pa at the time offorming the carbon film. Accordingly, it is possible to make the carbonprotective film thinner while also maintaining a sufficient durability,and thus to provide a magnetic recording medium that is capable ofreducing spacing loss at the time of recording and replay.

Therefore, it is possible to provide a highly reliable magneticrecording medium, which can support a sufficiently high recordingdensity without lowering the output properties thereof.

In addition, it is also possible to increase the coating rate, andproduction efficiency.

In the following, another embodiment of the method for manufacturing amagnetic recording medium according to the present invention, using anexample in which the aforementioned plasma CVD apparatus shown in FIG. 1is employed.

Initially, a non-magnetic base film and magnetic film were formed onboth sides of a non-magnetic substrate, according to a method such as aspatter-coating method or the like, to obtain a disc D.

The non-magnetic substrate may comprise any substrate that is generallyused as a substrate for a magnetic recording medium, as described in theaforementioned. The material and thickness of the non-magnetic base filmand magnetic film are also as described in the aforementioned.

Subsequently, the disc D is transported into the chamber 10 of theaforementioned plasma CVD apparatus, and the surface of the disc D isexposed to the reactant gas, which is supplied from the supply source 14through the introduction tube 15 into the chamber 10. The gas is thenexhausted from chamber 10 via the exhaust tube 16 to circulate the gastherein.

According to the manufacturing method of this embodiment, the reactantgas is that comprises a mixed gas of hydrocarbon and hydrogen, with amixing ratio of hydrocarbon to hydrogen in the range of 2 to 1˜1 to 100by volume, into which nitrogen gas is added at a adding volume of0.1˜100% of the mixed gas, and preferably 50˜100 vol %.

The hydrocarbon preferably comprises at least one type of hydrocarbonselected from among lower saturated hydrocarbons, lower unsaturatedhydrocarbons, and lower cyclic hydrocarbons.

The nitrogen gas is added into the aforementioned mixed gas at a addingvolume of 0.1˜100% of the mixed gas. A adding volume of the nitrogen gasto the mixed gas of less than 0.1% by volume, or alternatively exceeding100% by volume reduces the hardness of the carbon protective film, whichin turn leads to an insufficient durability.

In addition, the reason that the mixing ratio of the aforementionedmixed gas of hydrocarbon to hydrogen is preferably in the aforementionedrange since a mixing ratio of the hydrocarbon to hydrogen in the mixedgas of less than the aforementioned range leads to a reduced coatingrate which is unsuitable for practical, industrial production.Similarly, a mixing ratio exceeding the aforementioned range results inan increase in the stress remaining within the carbon protective film,leading to inferior adhesion and an inferior resistance to CSS in theresultant carbon protective film.

In addition, a lower hydrocarbon is preferably used as thehydrocarbon—if the number of carbon atoms of the hydrocarbon exceeds theaforementioned range, it is difficult to supply the hydrocarbon as agas, and in addition, at the time of discharge, difficulty with thedecomposition of hydrocarbons is encountered, which in turn leads to acarbon protective film containing high polymers that are inferior instrength.

When carrying out the operation, the flow rate of the reactant gas ispreferably in the range of 50˜500 sccm. In addition, the inner pressureof the chamber 10 is preferably set at the predetermined value, e.g.,0.1˜10 Pa.

At the same time, high frequency electrical power of preferably 50˜2000W is supplied to the electrodes 11, using the high frequency electricalpower source 12, to generate plasma, and thereby form a carbonprotective film on both sides of the disc D by means of plasma chemicalgas phase growth, using the aforementioned reactant gas as a startingmaterial. The thickness of the carbon protective film is preferably inthe range of 30˜100 Å.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode 11 different. By means of shifting the phase of electricalpower supplied to each electrode, it is possible to improve both thecoating rate and durability of the protective film. The difference inthe phase of electrical power supplied to each electrode is preferablyin the range of 90˜270°, and in particular the opposite phase (i.e.,180°) is preferred.

In addition, when forming the carbon protective film, it is preferableto form the film while performing bias applying, such as high frequencybias or pulse D.C. bias, to the disc D, using the electrical bias source13.

The conditions of bias such as voltage and the like are preferably asdescribed in the aforementioned.

In addition, a lubricating film may be provided on the protective filmby means of applying the aforementioned lubricant.

In the aforementioned manufacturing method, as the reactant gas, bymeans of adding a nitrogen gas, at a adding volume of 0.1˜100% of themixed gas, and preferably 50˜100% by volume, into the mixed gascomprising hydrocarbon and hydrogen, with a mixing ratio of hydrocarbonto hydrogen in the range of 2 to 1˜1 to 100 by volume, at the time offorming the carbon protective film, the carbon protective film exhibitsa superior durability. Accordingly, it is possible to make the carbonprotective film thinner while maintaining a sufficient durability, andthus provide a magnetic recording medium that is capable of reducingspacing loss at the time of recording and replay.

Therefore, it is possible to provide a highly reliable magneticrecording medium, which can support a sufficiently high recordingdensity without lowering the output properties thereof.

The reason that it is possible to form a carbon protective filmpossessing a superior durability by means of using a mixed gas, in whichthe nitrogen gas has been added at a adding volume of 0.1˜100% of themixed gas as the reactant gas at the time of forming the aforementionedcarbon protective film, is unclear, but is hypothesized as follows.

It is hypothesized that by means of using gas containing nitrogen gas asthe reactant gas, the nitrogen atoms bond to “dangling bonds” whichexists in the carbon protective film, thereby increasing the chemicalstability and mechanical strength of the carbon protective film.

Additionally, in particular, when providing a lubricating film on thecarbon protective film, by means of using a reactant gas containingnitrogen gas, the wetting properties on the surface of the carbonprotective film are improved due to the introduction of the nitrogenpolar groups. Accordingly, the affinity of the carbon protective film tothe lubricating film improves, leading to improved durability of themagnetic recording medium.

The reason for setting the adding volume of nitrogen gas to the mixedgas in the aforementioned range is that if the adding volume is lessthan the aforementioned range, the aforementioned effects becomeinsufficient, while if the adding volume exceeds the aforementionedrange, the nitrogen content in the carbon protective film becomes toohigh, leading to a decrease in the strength of the carbon protectivefilm, and inferior durability.

In the following, the effects of the present invention are specified,using concrete examples.

TEST EXAMPLES 46 AND 47

After an aluminium alloy substrate coated with a NiP metal film (with adiameter of 95 mm and thickness of 0.8 mm) was treated with mechanicaltexture-processing to form an average surface roughness of 20 Å, anon-magnetic base film (with a thickness of 600 Å) comprising a Cralloy, and a magnetic film comprising a Co alloy were successivelyformed on both sides of the substrate, using a spattering device (3010manufactured by Anelva), to obtain a disc D.

Subsequently, the disc D was transported into the chamber 10 of theaforementioned plasma CVD apparatus, and a reactant gas was suppliedfrom the supply source 14 into the chamber to achieve a flow rate of 130sccm.

A mixed gas of toluene and hydrogen, with a mixing ratio of toluene tohydrogen of 1 to 10 by volume, into which nitrogen gas was added at aadding volume shown in Table 6, was used as the reactant gas.Furthermore, the inner pressure of the chamber 10 was maintained at 6Pa.

At the same time, high frequency electrical power of 500 W was suppliedto the electrodes 11 to generate plasma, and thereby form the carbonprotective film with a thickness of 50 Å on both sides of the disc D. Atthis time, high frequency electrical power of 50 W was applied to thedisc D, using the electrical bias source 13. In addition, the differencein the phase of high frequency electrical power supplied to eachelectrode 11 was set at 180°.

Subsequently, fomblin lubricant was applied to the carbon protectivefilm, to form a lubricating film with a thickness of 15 Å, therebyyielding the magnetic recording medium.

The CSS test and corrosion test the following were performed on themagnetic recording media.

In the CSS test, using an MR head, a CSS operation was performed 20,000times at a rotational speed of 7200 rpm, and a temperature of 40° C.with a humidity of 80%. The dynamic stiction value was monitored afterallowing the magnetic recording medium to sit for one hour.

In the corrosion test, after sitting for 96 hours at a high temperature(60° C.) and high humidity (80%), the magnetic recording medium wassoaked in 50 cc of ultrapure water at 25° C., and the extraction amountof Co (per substrate area) from the ultrapure water was measured. Inaddition, the extraction amount of Co was measured in the same mannerafter allowing the magnetic recording medium to sit for 96 hours atnormal temperature (25° C.) and normal humidity (50%). These testresults are shown in Table 6.

TEST EXAMPLES 48 AND 49

Magnetic recording medium was manufactured, using a gas, in whichnitrogen gas had been added into a mixed gas at a adding volume shown inTable 6, as the reactant gas. The CSS test and corrosion test wereperformed on the magnetic recording media. These test results are alsoshown in Table 6.

TABLE 6 Adding Corrosion test vol. of Normal nitrogen Coating temp. &High temp. gas Stiction rate humidity & humidity (vol. %) (−) (Å/min)(ng/cm²) (ng/cm²) Test Example 46 50 0.88 664 0.07 0.34 Test Example 47100 0.67 432 0.11 0.25 Test Example 48 0 1.27 753 0.12 0.24 Test Example49 200 Crash 125 0.44 1.25

From Table 6, it is clear that the magnetic recording media manufacturedaccording to a method which used a mixed gas, into which nitrogen gaswas added at a adding volume of 0.1˜100% of the mixed gas, as thereactant gas, exhibited lower stiction values, leading to a superiordurability. Additionally, from the results of the corrosion test, it isclear that these magnetic recording media contained only an extremelysmall amount of corrosion, and exhibited a level of resistance tocorrosion which poses no problem for practical use.

As explained in the aforementioned, in the method for manufacturing amagnetic recording medium according to the present invention, it ispossible to form a carbon protective film comprising a superiordurability. Accordingly, it is possible to make the carbon protectivefilm thinner while also maintaining a sufficient durability, and hencereduce spacing loss.

Thus, it is possible to provide a highly reliable magnetic recordingmedium, which can support a sufficiently high recording density withoutlowering the output properties thereof.

In the following, an embodiment of the magnetic recording mediumaccording to the present invention is described. FIG. 4 shows anembodiment of the magnetic recording medium according to the presentinvention, wherein a non-magnetic base film 41, magnetic film 42, carbonprotective film 43, and lubricating film 44 are successively formed on anon-magnetic substrate S.

The non-magnetic substrate S may comprise any substrate that isgenerally used as a substrate for a magnetic recording medium, examplesof which may include an aluminium alloy substrate coated with a NiPmetal film, and substrates comprising glass, silicone, and the like.

In addition, the surface of the non-magnetic substrate S is preferablytreated with texture-processing, e.g., mechanical texture-processing. Inparticular, the average surface roughness (Ra) is preferably in therange of 1˜20 Å.

Preferred examples of the materials for the non-magnetic base film 41and magnetic film 42 are as described in the aforementioned.

The thickness of the non-magnetic base film 41 and magnetic film 42 ispreferably in the range of 50˜1000 Å, and 50˜800 Å, respectively.

In the magnetic recording medium according to the present invention, thecarbon protective film may comprise a two-layer structure, comprising aplasma CVD carbon layer 43 a formed according to a plasma CVD method,and a spatter carbon layer 43 b formed thereon according to aspatter-coating method.

The thickness of a plasma CVD carbon layer 43 a is preferably in therange of 30˜100 Å.

A thickness of less than 30 Å results in an insufficient strength forthe entire protective film; while a thickness exceeding 100 Å results ina magnetic recording medium with a greater spacing loss at the time ofrecording and replay, which leads to a higher likelihood of loweringoutput properties when increasing recording density.

The spatter carbon layer 43 b is provided on the surface of the carbonprotective film 43, and its thickness is in the range of 5˜100 Å, andpreferably 30˜100 Å.

A thickness of less than 5 Å results in weakening of the bonds betweenthe spatter carbon layer 43 b and lubricating film 44, leading to aninferior resistance to sliding of the magnetic recording medium. On theother hand, a thickness exceeding 100 Å results in a decrease in theoutput properties at the time of increasing recording density.

Preferred examples of the materials of the lubricating film 44 mayinclude perfluoropolyether, fomblin lubricant, and the like. Thethickness of the lubricating film 44 is preferably 5˜40 Å.

In the following, another embodiment of the method for manufacturing amagnetic recording medium according to the present invention isdescribed, using an example in which an aforementioned magneticrecording medium is manufactured.

FIG. 5 shows the spatter equipment used for manufacturing theaforementioned magnetic recording medium, which comprises a chamber 50,targets 51, which are provided on the inner walls on both sides of thechamber 50; an electrical source 52 which supplies electrical power tothe targets 51; a supply source 53 for spatter gas which suppliesspatter gas into the chamber 50.

The chamber 50 is connected to a introduction tube 54 which directs thespatter gas supplied from the supply source 53 into the chamber 50, andan exhaust tube 55 which expels gas inside of the chamber 7 out of thesystem.

The target 51 may principally comprise carbon.

The electrical source 52 may comprise a D.C. electrical source, or ahigh frequency electrical source.

In order to manufacture the aforementioned magnetic recording mediumusing the aforementioned spatter equipment and plasma CVD apparatusshown in FIG. 1, a non-magnetic base film 41 comprising a Cr alloy, andmagnetic film 42 comprising a Co alloy are successively formed on bothsides of an aluminium alloy substrate S coated with a NiP metal film,according to a method such as a spatter-coating method, to obtain a discD.

Subsequently, the disc D is transported into the chamber 10 of theaforementioned plasma CVD apparatus, and the surface of the disc D isexposed to the reactant gas, which is supplied from the supply source 14via the introduction tube 15 into the chamber 10, from which gas isexhausted via the exhaust tube 16 to circulate the gas within.

The reactant gas is preferably a mixed gas of hydrocarbon and hydrogen,with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1˜1to 100 by volume, and the hydrocarbon preferably comprises at least onetype of hydrocarbon selected from among lower saturated hydrocarbons,lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.

When carrying out this operation, the flow rate of the reactant gas ispreferably 50˜500 sccm. Additionally, the inner pressure of the chamber10 is preferably set at a predetermined value, such as 0.1˜10 Pa.

At the same time, using the high frequency electrical power source 12,high frequency electrical power of preferably 50˜2000 W is supplied tothe electrodes 11 to generate plasma, and a plasma CVD carbon layer 43a, the thickness of which is preferably in the range of 30˜100 Å, isformed on both sides of the disc D by means of plasma chemical gas phasegrowth, using the aforementioned reactant gas as a starting material.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode 11 different. By means of making the phases of electricalpower supplied to each electrode 11 different, it is possible to improvethe coating rate and durability of the protective film. The differencein the phase of electrical power supplied to each electrode ispreferably in the range of 90˜270°, and more preferably comprises theopposite phase (i.e., 180°).

In addition, it is preferable to form the film while performing biasapplying, such as high frequency bias or pulse D.C. bias, to the disc D,using the electrical bias source 13. When using high frequencyelectrical source as the electrical bias source 13, high frequencyelectrical power of 10˜300 W is preferably applied to the disc D.Additionally, when using pulse D.C. electrical source as the electricalbias source 13, a voltage of −400˜−10V is preferably applied to the discD. Furthermore, the width of pulse is preferably in the range of10˜50000 ns, and the frequency is preferably in the range of 10 kHz˜1GHz.

The resultant plasma CVD carbon layer 43 a contains a higher content ofdiamond-like carbon (DLC) of an increased hardness, and is superior instrength, when compared to the carbon films formed according to theconventionally known, spatter-coating method.

Subsequently, the disc D, on the surface of which a plasma CVD carbonlayer 43 a has been formed according to the aforementioned operation, istransported into the chamber 50 of the spatter equipment, and thesurface of the plasma CVD carbon layer 43 a, formed on theaforementioned disc D, is exposed to the spatter gas, which is suppliedinto chamber 50 from the supply source 53 via the introduction tube 54.Gas is then exhausted via the exhaust tube 55 to circulate the gaswithin.

The spatter gas may comprise argon, which is generally used in thespatter-coating method. In particular, a mixed gas comprising argon,into which at least one gas selected from among nitrogen, hydrogen, andmethane is added at a adding volume to the argon of 0.1˜100% by volume,is preferred.

At the same time, electrical power is supplied to target 51, using theelectrical source 52, and the material of target 51 is then suppliedonto the plasma CVD carbon layer 43 a by means of spattering, to formthe spatter carbon layers 43 b on both sides of the disc D.

In this operation, the flow rate of the spatter gas is preferably 20˜300sccm.

Subsequently, a lubricant such as perfluoropolyether, fomblin lubricant,and the like, is applied to the spatter carbon layer 43 b, according toa dipping method or the like.

In this manner, a magnetic recording medium, which comprising anon-magnetic base film 41, magnetic film 42, carbon protective layer 43which comprises plasma CVD carbon layer 43 a and spatter carbon layer 43b, and lubricating layer 44 are successively formed on the substrate S,is provided.

In the aforementioned magnetic recording medium, since the carbonprotective layer 43 is provided with a plasma CVD carbon layer 43 aformed according to a plasma CVD method, and spatter carbon layer 43 bformed according to a spatter-coating method, the adhesion of thelubricating film 44 to the carbon protective film 43 is increased, whichleads to a superior durability.

It is hypothesized that the spatter carbon layer 43 b formed by means ofspattering has a greater number of “dangling bonds” when compared to thecarbon film formed according to the plasma CVD method. Therefore,bonding which involves the “dangling bond” creates a stronger adhesionto the lubricating film 44, and thus leads to the superior durability ofthe aforementioned magnetic recording medium.

In addition, since the carbon protective layer 43 possesses a plasma CVDcarbon layer 43 a of superior strength, it is possible to make thecarbon protective film 43 thinner while also maintaining the durability,and thus reduce spacing loss. In addition, it is possible to preventproblems such as “spin-off” in CSS operation.

Accordingly, it is possible to provide effects of reliability and asufficiently high recording density, without lowering the outputproperties thereof. Furthermore, in the aforementioned embodiment, thecarbon protective layer 43 is provided with a two-layer structurecomprising the plasma CVD carbon layer 43 a and spatter carbon layer 43b. However, the magnetic recording medium according to the presentinvention is not limited thereto, and may also comprise a structurepossessing three or more layers.

In the following, the effects of the present invention are specified,using concrete examples.

TEST EXAMPLES 50˜52

A magnetic recording medium was manufactured as follows, using theplasma CVD apparatus and spatter equipment shown in FIGS. 1 and 5.

After an aluminium alloy substrate coated with a NiP metal film (with adiameter of 95 mm and thickness of 0.8 mm) was treated with mechanicaltexture-processing to form an average surface roughness of 20 Å, anon-magnetic base film 41 (with a thickness of 600 Å) comprising a Cralloy, and a magnetic film 42 comprising a Co alloy (Co₈₂Cr₁₅Ta₃) weresuccessively formed on both sides of the substrate S, using a spatteringdevice (3010 manufactured by Anelva), to obtain a disc D.

Subsequently, the disc D was transported into the chamber 10 of theplasma CVD apparatus, and a reactant gas was supplied from the supplysource 14 into the chamber to achieve a flow rate of 130 sccm.

A mixed gas of toluene and hydrogen, with a mixing ratio of toluene tohydrogen of 1 to 10 by volume, was used as the reactant gas.Additionally, the inner pressure of the chamber 10 was maintained at 6Pa.

At the same time, high frequency electrical power of 500 W was suppliedto the electrodes 11 to generate plasma, and thereby form a plasma CVDcarbon layer 43 a with a thickness of 40 Å on both sides of the disc D.At this time, pulse D.C. bias of −120V (with a frequency of 200 kHz andpulse width of 500 ns) was applied to the disc, using the electricalbias source 13. Furthermore, the temperature of the disc D at the timeof coating was maintained at 150° C. The difference in the phase of highfrequency electrical power supplied to each electrode 11 was set at180°. In addition, the distance between the disc D and electrode 11 wasset at 30 mm.

Subsequently, the disc D, on the surface of which the plasma CVD carbonlayer 43 a was formed according to the aforementioned operation, wastransported into the chamber 50 of the spatter equipment, and thespatter gas supplied from the supply source 53 was directed into thechamber 50 via the introduction tube 54.

Spatter gas containing the respective components shown in Table 7 wasused herein.

At the same time, electrical power was supplied to the target 51, usingthe electrical source 52, and the spatter carbon layers 43 b were formedon both sides of the disc D, by means of spattering.

Subsequently, a fomblin lubricant (Fomblin Zdol 2000) was applied ontothe spatter carbon layer 43 b, according to a dipping method, and alubricating film 44 with a thickness of 20 Å was formed, therebyyielding a magnetic recording medium.

The “bonded ratio” test, “spin-off” test, and CSS test described in thefollowing were performed on resultant magnetic recording media.

(1) Bonded Ratio Test

The aforementioned magnetic recording medium was soaked in a solvent(AK225 manufactured by Asahi Glass) for 15 minutes, and then removed.The ratio of the thickness of the lubricating film 44 prior to thisoperation and after this operation was then calculated in percentage.The thickness of the lubricating film 44 was measured at the positionwhere the radius was 20 mm, using ESCA.

(2) Spin-off Test

The aforementioned magnetic recording medium was rotated at a rotationalspeed of 10000 rpm and a temperature of 100° C. for 168 hours. The ratioof the thickness of the lubricating film 44 prior to this operation andafter this operation was then calculated in percentage. The thickness ofthe lubricating film 44 was measured at the positions, where the radiusof the magnetic recording medium was 20 mm (inner circumference) and 42mm (outer circumference), using FT-IR.

(3) CSS Test

Using an MR head, a CSS operation was performed on the aforementionedmagnetic recording medium 80000 times, at a rotational speed of 7200rpm, and a temperature of 40° C. at a humidity of 80%.

These test results are shown in Table 7.

TEST EXAMPLES 53 AND 54

A carbon protective film was formed according to only a plasma CVDmethod, based on the methods in TEST EXAMPLES 50˜52, to provide amagnetic recording medium comprising a carbon protective film comprisinga single-layer structure (Test Example 53).

In addition, a carbon protective film was formed according to aconventionally known, spatter-coating method, to provide a magneticrecording medium comprising a carbon protective film comprising asingle-layer structure. (Test Example 54)

The aforementioned three types of tests were performed on these magneticrecording media. These test results are shown in Table 8.

In the tables, the plasma CVD carbon layer is represented as “pCVDlayer”, and the spatter carbon layer is represented as “spatter layer”.

TABLE 7 Spin-off Spin-off Structure Thick- Thick- Inner Outer of ness ofness of Bonded circum- circum- protective pCVD spatter Spatter ratioference ference film layer (Å) layer (Å) gas (%) (%) (%) CSS TestTwo-layer 40 10 100% Ar 38 58 64 No Example 50 crash Test Two-layer 4010 98% Ar 46 65 74 No Example 51 and 2% crash N₂ Test Two-layer 40 1090% Ar 16 48 55 No Example 52 and 10% crash CH₄

TABLE 8 Spin-off Spin-off Structure Coating Thick- inner outer of methodness of Bonded circum- circum- protective of carbon carbon Spatter ratioference ference film film film (Å) gas (%) (%) (%) CSS Test Single- pCVD50 — 20 37 43 Crash Example 53 layer Test Single- Spatter- 100 100% Ar42 77 84 Crash Example 54 layer coating

From the results of the CSS test shown in Tables 7 and 8, it is clearthat the magnetic recording media in which the carbon protective film 43comprised a two-layer structure comprising the plasma CVD carbon layer43 a and spatter carbon layer 43 b exhibited sufficient durabilityagainst CSS operation performed over 80000 times, whereas the magneticrecording media in which the carbon protective film comprised asingle-layer structure formed according to only a plasma CVD method, orspatter-coating method, led to “head crash”.

Additionally, from the results of the bonded ratio test and spin-offtest, it is clear that the magnetic recording medium wherein the carbonprotective film 43 comprised a two-layer structure exhibited a lowerreduction ratio of the thickness of the lubricating film, compared tothe magnetic recording medium wherein the carbon protective film wasformed only according to the plasma CVD method.

Accordingly, the magnetic recording media in which the carbon protectivefilm 43 comprised a two-layer structure exhibited a superior durabilitywhen compared to the magnetic recording medium in which the carbonprotective layer comprised a single-layer structure formed according toonly a plasma CVD method, or spatter-coating method.

As explained in the aforementioned, according to the present invention,it is possible to form a carbon protective film with a superiordurability. As a result, it is also possible to make the carbonprotective film thinner while also maintaining a sufficient durability,and thereby reduce spacing loss.

Therefore, it is possible to provide a highly reliable magneticrecording medium, which is capable of sufficiently increasing recordingdensity without lowering the output properties thereof.

In the following, another embodiment of the method of manufacturing themagnetic recording medium according to the present invention, using anexample in which the plasma CVD apparatus shown in FIG. 1 is employed.

Initially, a non-magnetic base film and magnetic film are respectivelyformed on both sides of the non-magnetic substrate according to a methodsuch as a spatter-coating method, and the like, to obtain a disc D.

The non-magnetic substrate may comprise any substrate that is generallyused as a substrate for magnetic recording medium as described in theaforementioned. The material and thickness of the non-magnetic base filmand magnetic film are as described in the aforementioned.

In the method for manufacturing the magnetic recording medium accordingto the present embodiment, the process of coating the carbon protectivefilm comprises two subsequent processes as described in the following.

As the first process, the following operation is performed.

The disc D, wherein the non-magnetic base film and magnetic film areformed on the aforementioned non-magnetic substrate, is transported intothe chamber 10 of the plasma CVD apparatus, and the surface of the discD is exposed to the reactant gas, which is supplied from the supplysource 14 through the introduction tube 15 into the chamber 10. The gasis then exhausted from chamber 10 via the exhaust tube 16 to circulatethe gas therein.

The reactant gas is, as described in the aforementioned, preferably amixed gas of hydrocarbon and hydrogen, with a mixing ratio ofhydrocarbon to hydrogen in the range of 2 to 1˜1 to 100 by volume. Thehydrocarbon preferably comprises at least one type of hydrocarbonselected from among lower saturated hydrocarbons, lower unsaturatedhydrocarbons, and lower cyclic hydrocarbons.

In this operation, the flow rate of the reactant gas is preferably inthe range of 50˜500 sccm. Additionally, the inner pressure of thechamber 10 is preferably set at a predetermined value such as 0.1˜10 Pa.

At the same time, high frequency electrical power of preferably 50˜2000W is supplied to electrodes 11, using a high frequency electrical source12, to generate plasma, and the first carbon layer having a thickness ofpreferably 30˜45 Å is formed on both sides of the disc D by means ofplasma chemical gas phase growth, using the aforementioned reactant gasas a starting material.

In this first process, at this point, bias such as high frequency biasor pulse D.C. bias is applied to the disc D, to form the film by meansof a bias electrical source 13.

When using high frequency bias as the aforementioned bias, highfrequency electrical power of 10˜300 W is preferably applied to thedisc, using a high frequency electrical source as the bias electricalsource 13.

This is due to the fact that if bias applied to the disc D duringcoating is less than 10 W, the first carbon layer will contain a largeamount of high polymer components, which are inferior in strength, andthus reduce the durability. On the other hand, if the bias exceeds 300W, sparks are likely to occur during coating, which lead to a greaterlikelihood of creating abnormal growth sections on the surface of thefirst carbon layer.

Additionally, when using pulse D.C. bias as bias and pulse D.C.electrical source as the bias electrical source 13, a voltage of−400˜−10 V is preferably applied to the disc.

This is due to the fact that if bias applied to the disc D duringcoating is less than −400 V, sparks are likely to occur at the time ofcoating, which lead to a greater likelihood of creating abnormal growthsections on the surface of the first carbon layer. If the bias exceeds−10 V, the first carbon layer contains a higher content of high polymercomponents, which are inferior in strength.

In addition, preferably, the pulse width is in the range of 10˜50000 ns,and the frequency is in the range of 10 kHz˜1 GHz.

The resultant first carbon layer thereby contains a large amount ofdiamond-like-carbons (DLC) which exhibit an increased hardness.

The reason for preferably setting the thickness of the first carbonlayer in the range of 30˜45 Å is due to the fact that a thickness ofless than 30 Å results in a reduction in the strength of the carbonprotective film, leading to a lower durability of the resultant magneticrecording medium; and a thickness exceeding 45 Å results in a magneticrecording medium that exhibits greater spacing loss at the time ofrecording and replay, which tends to lower output properties at the timeof increasing the recording density.

Subsequently, the second process described in the following isperformed.

In the second process, bias applying to the disc D, using the biaselectrical source 13, is halted, and a second carbon layer of preferably5˜20 Å is formed onto the first carbon layer in a similar manner as inthe aforementioned first process, with the exception that bias applyingis not performed.

The reason for setting the thickness of the second carbon layer in therange of 5˜20 Å is due to the fact that if the thickness is less than 5Å, the joining strength between the second carbon layer and lubricatingfilm weakens, leading to a lower resistance to sliding of the magneticrecording medium; while if the thickness exceeds 20 Å, the resultantmagnetic recording medium exhibits greater spacing loss at the time ofrecording and replay, which tends to lower output properties at the timeof increasing the recording density.

In the aforementioned first and second processes, when supplyingelectrical power to the electrodes 11 and 11, the phase of theelectrical power supplied to each electrode 11 are preferably shiftedwith respect to each other. By means of making the phases of electricalpower supplied to each electrode 11 different, it is possible to improveboth the coating rate and durability of the protective film. Thedifference of the phase of electrical power supplied to each electrodeis preferably in the range of 90˜270°, and in particular, the oppositephase (i.e., 180°) is preferred.

Through the aforementioned first and second processes, the carbonprotective film comprising the first and second carbon layer is formedonto the disc D.

Subsequently, a lubricant such as perfluoropolyether, fomblin lubricant,and the like, is applied onto the second carbon layer according to adipping method or the like, to form a lubricating film with a thicknessof preferably 5˜40 Å.

In this manner, a magnetic recording medium is obtained, wherein anon-magnetic base film, magnetic film, a carbon protective film (firstcarbon layer and second carbon layer), and lubricating film aresuccessively formed.

Examples of the magnetic recording medium manufactured according to theaforementioned manufacturing method may include a magnetic recordingmedium with a structure similar to that shown in FIG. 4.

The magnetic recording medium of this example comprises a non-magneticsubstrate S, non-magnetic base film 41, magnetic film 42, carbonprotective film 43 (first carbon layer 43 a, and second carbon layer 43b), and lubricating film 44.

In the aforementioned method for manufacturing a magnetic recordingmedium, the carbon protective film 43 is formed, by means of forming asecond carbon layer 43 b, according to the plasma CVD method withoutperforming bias applying to the disc D, on top of a first carbon layer43 a, which is formed according to a plasma CVD method while performingbias applying to the disc D. In this manner, the resultant magneticrecording medium exhibits a higher bonding strength with respect to thelubricating film 44, lying in contact with the second carbon layer 43 bof the carbon protective film 43, and hence leads to a superiordurability.

The reason for the superior durability of the aforementioned magneticrecording medium is as follows. That is, the second carbon layer 43 b,which is formed without performing bias applying to the disc D, containsa greater number of dangling bonds, compared to the first carbon layer43 a which is formed while performing bias applying to the disc D, andbonding which involves these dangling bond generates a stronger adhesionto the lubricating film.

In addition, the first carbon layer 43 a, which is formed whileperforming bias applying to the disc D contains a higher content ofdiamond-like-carbon (DLC), leading to a superior strength.

As a result, the carbon protective film 43 exhibits a higher strength,and moreover is firmly joined to the lubricating film 44. Accordingly,it is possible to make the carbon protective film 43 thinner while alsomaintaining a sufficient durability, and thereby reduce spacing loss.Additionally, problems such as spin-off in the CSS operation do notoccur.

Accordingly, it is possible to provide a highly reliable magneticrecording medium that is capable of increasing the recording densitysufficiently without lowering the output properties thereof.

Furthermore, in the aforementioned embodiment, the carbon protectivefilm comprises a two-layer structure comprising a first carbon layer 43a and second carbon layer 43 b. However, the magnetic recording mediumaccording to the present invention is not limited thereto, and maycomprise a structure of three or more layers.

In the following, the effects of the present invention are specified,using concrete examples.

TEST EXAMPLES 55˜59

Magnetic recording medium was manufactured as described in thefollowing, using the plasma CVD apparatus shown in FIG. 1.

After an aluminium alloy substrate coated with a NiP metal film (with adiameter of 95 mm and thickness of 0.8 mm) was treated with mechanicaltexture-processing to form an average surface roughness of 20 Å, anon-magnetic base film 41 (with a thickness of 600 Å) comprising a Cralloy, and a magnetic film 42 comprising a Co alloy (Co₈₂Cr₁₅Ta₃) weresuccessively formed on both sides of the substrate S, using a spatteringdevice (3010 manufactured by Anelva), to obtain a disc D.

Subsequently, the disc D was transported into the chamber 10 of theplasma CVD apparatus, and a mixed gas was supplied from the supplysource 14 into the chamber to achieve a flow rate of 130 sccm.

A mixed gas of toluene and hydrogen, with a mixing ratio of toluene tohydrogen of 1 to 12 by volume, was used as the reactant gas.Additionally, the inner pressure of the chamber 10 was maintained at 6Pa.

At the same time, high frequency electrical power of 450 W was suppliedto the electrodes 11 to generate plasma, while applying pulse D.C. biasof −120V (with a frequency of 200 kHz and a pulse width of 500 ns) tothe disc D, using the bias electrical source 13, to form the firstcarbon layer 43 a. The temperature of the disc D and coating rate at thetime of coating were set at 130° C., and 450 Å/min, respectively. Thedifference in the phase of high frequency electrical power supplied toeach electrode 11 was set at 180°. In addition, the distance between thedisc D and electrode 11 was set at 30 mm.

Subsequently, a second carbon layer 43 b with a thickness shown in Table9 was formed onto the disc D, onto which a first carbon layer 43 a hadbeen formed on the surface thereof as described in the aforementioned,according to the similar method for forming the first carbon layer 43 a,with the exception that bias was not applied to the disc D.

Subsequently, a fomblin lubricant (Fomblin Zdol 2000) was applied ontothe second carbon layer 43 b, according to a dipping method, and alubricating film 44 with a thickness of 20 Åwas formed, thereby yieldinga magnetic recording medium.

The bonded ratio test, spin-off test, and CSS test described in thefollowing were then performed on the resultant magnetic recording media.

(1) Bonded Ratio Test

The aforementioned magnetic recording medium was soaked in a solvent(AK225 manufactured by Asahi Glass) for 15 minutes, and then removed.The ratio of the thickness of the lubricating film 44 prior to thisoperation and after this operation was then calculated in percentage.Furthermore, the thickness of the lubricating film 44 was measured at aposition where the radius was 20 mm, using ESCA.

(2) Spin-off Test

The aforementioned magnetic recording medium was rotated at a rotationalspeed of 10000 rpm and a temperature of 100° C. for 168 hours. The ratioof the thickness of the lubricating film 44 prior to this operation andafter this operation was then calculated in percentage. The thickness ofthe lubricating film 44 was measured at the positions where the radiusof the magnetic recording medium was 20 mm (inner circumference) and 42mm (outer circumference), respectively, using FT-IR.

(3) CSS Test

Using an MR head, a CSS operation was performed on the aforementionedmagnetic recording medium 40000 times at a rotational speed of 7200 rpm,and a temperature of 40° C. with a humidity of 80%.

The test results are shown in Table 9.

TEST EXAMPLE 60

A magnetic recording medium was manufactured in the similar manner as inthe aforementioned test example, with the exception that a second carbonlayer 43 b was not formed.

The resultant magnetic recording medium underwent with theaforementioned three types of tests. The test results are shown in Table9.

TEST EXAMPLE 61

A magnetic recording medium was manufactured, in which the carbonprotective film was formed according to a conventionally known,spatter-coating method.

The aforementioned three types of tests were performed on the resultantmagnetic recording medium. The test results are shown in Table 9.

TABLE 9 Spin-off Spin-off CSS (the First carbon layer Second carbonlayer Inner Outer number of Thick- Thick- Bond circum- circum- times aCoating ness Coating ness ratio ference ference crash method (Å) method(Å) (%) (%) (%) occurred) Test pCVD 40 pCVD 10 19 56 61 No crash Example55 (w/bias) (w/o bias) Test pCVD 32 pCVD 18 23 59 63 No crash Example 56(w/bias) (w/o bias) Test pCVD 25 pCVD 25 25 64 70 Crash Example 57(w/bias) (w/o bias) (37000) Test pCVD 12 pCVD 38 26 68 75 Crash Example58 (w/bias) (w/o bias) (25000) Test pCVD 47 pCVD 3 11 40 45 CrashExample 59 (w/bias) (w/o bias) (20000) Test pCVD 50 — — 10 38 44 CrashExample 60 (w/bias) (15000) Test Spatter- 50 — — 33 76 82 Crash Example61 ing

From the results of the CSS test shown in Table 9, it is clear that themagnetic recording media wherein the carbon protective film 43 compriseda first and second carbon layers 43 a and 43 b exhibited superiorresistance to sliding, when compared to the magnetic recording mediumwherein the carbon protective film comprised only a single-layerstructure.

In particular, the magnetic recording media wherein the thickness of thesecond carbon layer was 5˜20 Å exhibited sufficient durability againstthe CSS operation.

Additionally, from the results of the bonded ratio test and spin-offtest, it is clear that the magnetic recording media in which the carbonprotective film 43 comprised a two-layer structure exhibited a lowerreduction ratio of the thickness of the lubricating film, when comparedto magnetic recording media wherein the carbon protective film compriseda single-layer structure.

Accordingly, the magnetic recording media in which the carbon protectivefilm comprised a two-layer structure exhibited a superior durability.

As explained in the aforementioned, according to the present invention,it is possible to form a carbon protective film with a superiordurability. Therefore, it is also possible to make the carbon protectivefilm thinner while also maintaining a sufficient durability, and therebyreduce spacing loss.

As a result, it is possible to provide a highly reliable magneticrecording medium, which is capable of sufficiently increasing therecording density without lowering the output properties thereof.

In the following, another embodiment of the magnetic recording mediumaccording to the present invention is described.

The magnetic recording medium of this embodiment may comprise a similarstructure to that shown in FIG. 4. The magnetic recording mediumaccording to this embodiment comprises a non-magnetic substrate S,non-magnetic base film 41, magnetic film 42, carbon protective film 43(first carbon layer 43 a, and second carbon layer 43 b), and lubricatingfilm 44.

Examples of the non-magnetic substrate S may include an aluminium alloysubstrate coated with a NiP metal film, and substrates comprising glass,silicone, and the like. The surface of the substrate S is preferablytreated with texture-processing such as mechanical texture-processing.In particular, the average surface roughness (Ra) is preferably in therange of 1˜20 Å. The material and thickness of the non-magnetic basefilm 41 and magnetic film 42 are as described in the aforementioned.

In the magnetic recording medium of the present embodiment, theprotective film 43 comprises a two layer structure comprising a tantalumnitrogen layer 43 a and carbon layer 43 b formed thereon.

The tantalum nitrogen layer 43 a comprises titanium and nitrogen,incorporating a material comprising a nitrogen content of 1˜30 at % asits main component.

A nitrogen content of less than 1 at % results in a loss of strength ofthe protective film 43, leading to a lower durability of the resultantmagnetic recording medium. Additionally, a nitrogen content exceeding 30at % also results in a decrease in the strength of the protective film43, similarly leading to a lower durability of the resultant magneticrecording medium.

The tantalum and nitrogen in the tantalum nitrogen layer 43 a exist inthe form of TaN, Ta₂N, Ta₃N₅, simple substance, or mixture thereof.

The thickness of the tantalum nitrogen layer 43 a is preferably in therange of 1˜95 Å.

A thickness of less than 1 Å results in a protective film comprising aninadequate strength, while a thickness exceeding 95 Å results in amagnetic recording medium that exhibits greater spacing loss at the timeof recording and replay, leading to a likelihood of lowering the outputproperties at the time of increasing the recording density.

The carbon layer 43 b is formed according to the plasma CVD method.

The thickness of the carbon layer 43 b is preferably in the range of5˜100 Å.

If the thickness is less than 5 Å, the bond between the carbon layer 43b and lubricating film 44 weakens, leading to a lower resistance tosliding of the magnetic recording medium. On the other hand, a thicknessexceeding 100 Å results in a decrease in the strength of the protectivefilm 43.

The lubricating film 44 preferably comprises a lubricant such asperfluoropolyether, fomblin lubricant, and the like. The thickness ofthe lubricating film is preferably in the range of 5˜40 Å.

In the following, another embodiment of the method for manufacturingmagnetic recording medium according to the present invention isdescribed, using an example in which the aforementioned magneticrecording medium is manufactured.

In the manufacturing method according to the present embodiment, aspattering device is employed with a similar structure to that shown inFIG. 5, with the exception that a material comprising principallytantalum, or a mixture of tantalum and nitrogen is used as the target51.

D.C. electrical source or high frequency electrical source may be usedas the electrical source 52. Preferred examples of the D.C. electricalsource may include one that is capable of supplying an electrical powerof 50˜6000 W to the target 51.

In order to manufacture the aforementioned magnetic recording medium,using the aforementioned spattering device, and the plasma CVD apparatusshown in FIG. 1, a non-magnetic base film 41 comprising a Cr alloy orthe like, and a magnetic film 42 comprising a Co alloy or the like aresuccessively formed on both sides of the aluminium alloy substrate Scoated with a NiP metal film, according to a method such as aspatter-coating method, to obtain a disc D.

Subsequently, the disc D is transported into the chamber 50 of theaforementioned spattering apparatus, and the surface of the disc D isexposed to the spatter gas, which is supplied from the supply source 53through the introduction tube 54 into the chamber 50, from which the gasis exhausted via the exhaust tube 55 to circulate the gas within.

Examples of the spatter gas may include any gas described below.

When using a target principally comprising tantalum as the target 51, agas formed from Ar or the like, which is generally used in thespatter-coating method, into which a nitrogen gas has been added atadding volume of 0.1˜100 vol % of said gas, may be used.

Furthermore, when using a target principally comprising tantalum andnitrogen as the target 51, a gas such as Ar, or similar gas to which anappropriate amount of nitrogen has been added, may be used.

At the same time, electrical power is supplied to the target 51, usingthe electrical source 52, and the material of the target 51 further issupplied onto the disc D by means of spattering, to form a tantalumnitrogen layer 43 a, which comprises a material comprising tantalum andnitrogen as its main component, on both side of the disc D.

In this operation, the flow rate of the spatter gas is preferably in therange of 10˜200 sccm.

Subsequently, the disc D comprising a tantalum nitrogen layer 43 a istransported into the chamber 10 of the plasma CVD apparatus, and thesurface of the disc D is exposed to a reactant gas, which is suppliedfrom the supply source 14 through the introduction tube 15 into thechamber 10. The gas is then exhausted from chamber 10 via the exhausttube 16 to circulate the gas therein.

The reactant gas is preferably a mixed gas of hydrocarbon and hydrogen,with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1˜1to 100 by volume, and the hydrocarbon preferably comprises at least onetype of hydrocarbon selected from among lower saturated hydrocarbons,lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.

In this operation, the flow rate of the reactant gas is preferably inthe range of 50˜500 sccm. Additionally, the inner pressure of thechamber 10 is preferably set at a predetermined value such as 0.1˜10 Pa.

At the same time, high frequency electrical power of preferably 50˜2000W is supplied to the electrodes 11, using the high frequency electricalsource 12, to generate plasma, and thereby form a carbon layer 43 b witha thickness of preferably 5˜10 Å on both sides of the disc D, by meansof plasma chemical gas phase growth, using the aforementioned reactantgas as a starting material.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode 11 different. By means of making the phases of electricalpower supplied to each electrode 11 different , it is possible toimprove the coating rate and durability of the protective film. Thedifference in the phase of electrical power supplied to each electrodeis preferably in the range of 90˜270°, and in particular, morepreferably opposite phase (i.e., 180°).

The resultant carbon layer 43 b contains a higher content ofdiamond-like-carbons (DLC), which exhibit an increased hardness, leadingto a superior strength when compared to a carbon film formed accordingto the conventionally known, spatter-coating method.

In this operation, it is preferable to form the film while performingbias applying e.g., high frequency bias and pulse D.C. bias to the discD, using the bias electrical source 13.

The conditions such as the voltage of the bias are preferably set asdescribed in the aforementioned.

Subsequently, a lubricant such as perfluoropolyether, fomblin lubricant,and the like, is applied onto the carbon layer 43 b, according to adipping method, and the like, to form a lubricating film 44. In thismanner, a magnetic recording medium is provided wherein a non-magneticbase film 41 and magnetic film 42 are first formed onto a substrate S,followed by successive formation of a protective film 43, comprising atantalum nitrogen layer 43 a and a carbon layer 43 b, and a lubricatingfilm 44 thereon.

In the aforementioned magnetic recording medium, the protective film 43is provided with the carbon layer 43 b, which is formed on a tantalumnitrogen layer 43 a, consisting principally of a material comprisingtantalic and nitrogen, according to a plasma CVD method, and thusexhibits a superior durability.

The reason that the aforementioned magnetic recording medium exhibits asuperior durability can be attributed to the formation of a protectivefilm 43 comprising a carbon layer 43 b, which exhibits sufficientstrength and relatively high bonding strength with the lubricating film44, onto a tantalum nitrogen layer 43 a which exhibits a great hardness.

Accordingly, it is possible to make the protective film 43 thinner whilealso maintaining a sufficient durability, and thereby reduce spacingloss.

Therefore, it is possible to provide a magnetic recording medium, thatis reliable and capable of sufficiently increasing the recording densitywithout lowering the output properties thereof.

Furthermore, in the aforementioned embodiment, the protective film 43 isprovided with a two-layer structure comprising a tantalum nitrogen layer43 a and a carbon layer 43 b. However, the magnetic recording mediumaccording to the present invention is not limited thereto, and may alsocomprise a structure having three or more layers.

In the following, the effects of the present invention are specified,using concrete examples.

TEST EXAMPLES 62˜64

A magnetic recording medium was manufactured, using the aforementionedplasma CVD apparatus, and spattering device, according to the followingprocess. A spattering device with a target 51 comprising tantalum wasused.

After an aluminium alloy substrate coated with a NiP metal film (with adiameter of 95 mm and thickness of 0.8 mm) was treated with mechanicaltexture-processing to form an average surface roughness of 20 Å, anon-magnetic base film 41 (with a thickness of 600 Å) comprising a Cralloy, and a magnetic film 42 comprising a Co alloy (Co₈₂Cr₁₅Ta₃) weresuccessively formed on both sides of the substrate S, using a spatteringdevice (3010 manufactured by Anelva), to obtain a disc D.

Subsequently, the disc D was transported into chamber 50 of thespattering device, and a spatter gas was supplied from the supply source53 to the chamber 50 via the introduction tube 54.

A mixed gas of nitrogen and argon, comprising a mixing ratio shown inTable 10, was used as the spatter gas. Additionally, the inner pressureof the chamber 50 was maintained at 0.7 Pa.

At the same time, D.C. electrical power of 600 W was supplied to thetarget 51, and a tantalum nitrogen layer 43 a comprising tantalum andnitrogen was formed on both sides of the disc D by means of spattering.

Subsequently, the disc D was transported into the chamber 10 of theplasma CVD apparatus, and a reactant gas was supplied from the supplysource 14 into the chamber 10.

A mixed gas of toluene and hydrogen, comprising a mixing ratio shown inTable 10, was used as the reactant gas. Additionally, the inner pressureof the chamber 10 was maintained at 6 Pa.

At the same time, high frequency electrical power of 300 W was suppliedto the electrodes 11, to generate plasma, while applying high frequencyelectrical power of 50 W (with a frequency of 13.56 MHz) to the disc D,using the bias electrical source 13, to form a carbon layer 43 b on bothsides of the disc D.

Furthermore, the temperature of the disc D at the time of forming thecarbon layer 43 b was set at 130° C. The difference in the phase of highfrequency electrical power supplied to each electrode 11 was 180°.Additionally, the distance between the disc D and the electrode 11 wasset at 30 mm.

Subsequently, a fomblin lubricant (Fomblin Zdol 2000) was applied ontothe carbon layer 43 b, according to a dipping method, to form alubricating film 44 with a thickness of 20 Å, thereby yielding amagnetic recording medium.

The CSS test described in the following was performed on the resultantmagnetic recording media. In the CSS test, using an MR head, a CSSoperation was performed 20000 times at a rotational speed of 7200 rpm,and a temperature of 40° C. with a humidity of 80%. The dynamic stictionvalue was monitored after allowing the magnetic recording medium to sitfor one hour. The results are shown in Table 10.

TEST EXAMPLE 65

A magnetic recording medium, wherein the protective film comprised asingle-layer structure comprising only a carbon layer, was manufacturedwithout forming a tantalum nitrogen layer.

TEST EXAMPLE 66

A magnetic recording medium, wherein the protective film comprised asingle-layer structure comprising only a tantalum nitrogen layer, wasmanufactured without forming a carbon layer.

TEST EXAMPLE 67

A magnetic recording medium, wherein the protective film comprised atwo-layer structure comprising a tantalum nitrogen layer and a carbonlayer, was manufactured according to a method in which a spatter gascontaining nitrogen, at a mixing ratio shown in Table 10, was used atthe time of forming the tantalum nitrogen layer.

The aforementioned CSS test was performed on these magnetic recordingmedia, and the test results are shown in Table 10.

The nitrogen content in the tantalum nitrogen layer of the magneticrecording medium in each of the aforementioned Test Examples 62, 63, 65,and 66 were 5 at %, and the nitrogen content in the tantalum nitrogenlayer of the magnetic recording medium in Test Example 67 was 40 at %.

TABLE 10 Structure Tantalic nitrogen layer Carbon layer of Nitrogencontent Thick- Flow rate of reactant gas Thick- protective in spattergas ness Toluene Hydrogen ness Stiction film (vol. %) (Å) (sccm) (sccm)(Å) (−) Test Two-layer 5 45 10 120 5 0.67 Example 62 Test Two-layer 5 1010 120 40 0.44 Example 63 Test Two-layer 5 45 100 0 5 0.91 Example 64Test Single- — — 10 120 50 1.27 Example 65 layer Test Single- 5 50 — — —Crash Example 66 layer Test Two-layer 50 30 109 120 20 Crash Example 67

From the results of the CSS test shown in Table 10, it is clear that themagnetic recording media comprising a protective film 43 comprising atantalum nitrogen layer 43 a, with a nitrogen content of 1˜30 at %, andcarbon layer 43 b formed thereon, exhibited sufficient durabilityagainst a CSS operation performed 20000 times. On the other hand, themagnetic recording media comprising only a single-layer carbonprotective film, or alternatively comprising a protective film in whichthe nitrogen content of the tantalum nitrogen layer was out of theaforementioned range, exhibited an inferior durability.

As explained in the aforementioned, according to the present invention,it is possible to form a carbon protective film with a superiordurability. Therefore, it is also possible to make the carbon protectivefilm thinner while also maintaining a sufficient durability, and therebyreduce spacing loss.

Thus, it is possible to provide a highly reliable magnetic recordingmedium, which is capable of sufficiently increasing the recordingdensity without lowering the output properties thereof.

FIGS. 6 and 7 show the critical parts of the manufacturing equipmentused in another embodiment of the method for manufacturing magneticrecording medium according to the present invention. FIG. 6 shows anultraviolet ray irradiation device; and FIG. 7 shows a washingapparatus.

The ultraviolet ray irradiation device is used to irradiate the surfaceof the carbon protective film with ultraviolet rays, and is providedwith a chamber 74 for storing a disc comprising a carbon protectivefilm; and ultraviolet ray source 75 for irradiating the surface of thedisc stored therein with ultraviolet rays. The ultraviolet ray source ispreferably one that is capable of irradiating ultraviolet rays with awavelength of 100˜400 nm.

Concrete examples of the ultraviolet ray source 75 may include anexcimer emission lamp.

The washing apparatus cleans the surface of the carbon protective filmof the disc, which has passed through the ultraviolet ray irradiationdevice, and is provided with a chamber 86 to store the disc; a supplysource 87 for cleaning water to clean the disc stored in the chamber 86;and a nozzle 88 for injecting cleaning water supplied from the supplysource 87 at the aforementioned disc.

In the following, another embodiment of the method for manufacturingmagnetic recording medium according to the present invention isdescribed, using an example in which the plasma CVD apparatus shown inFIG. 1 in addition to the aforementioned ultraviolet ray irradiationdevice and washing apparatus are employed.

Initially, a non-magnetic base film and magnetic film are formed on bothsides of non-magnetic substrate, according to the spatter-coating methodand the like, to obtain a disc D.

The non-magnetic substrate may comprise any substrate that is generallyused as a substrate for magnetic recording medium, as described in theaforementioned. The material and thickness of the non-magnetic base filmand magnetic film are as described in the aforementioned.

Subsequently, the disc D is transported into the chamber 10 of theaforementioned plasma CVD apparatus, and the surface of the disc D isexposed to a reactant gas, which is supplied from the supply source 14through the introduction tube 15 into the chamber 10. The gas is thenexhausted from chamber 10 via the exhaust tube 16 to circulate the gastherein.

The reactant gas is preferably a mixed gas of hydrocarbon and hydrogen,with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1˜1to 100 by volume, and the hydrocarbon preferably comprises at least onetype of hydrocarbon selected from among lower saturated hydrocarbons,lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.

When carrying out this operation, the flow rate of the reactant gas ispreferably 50˜500 sccm. Additionally, the inner pressure of the chamber10 is preferably set at a predetermined value, such as 0.1˜10 Pa.

At the same time, using the high frequency electrical power source 12,high frequency electrical power of preferably 50˜2000 W is supplied tothe electrodes 11 to generate plasma, and a carbon protective film, witha thickness preferably in the range of 30˜100 Å, is formed on both sidesof the disc D by means of plasma chemical gas phase growth, using theaforementioned reactant gas as a starting material.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode 11 different. By means of making the phases of electricalpower supplied to each electrode 11 different, it is possible to improvethe coating rate and durability of the protective film. The differencein the phase of electrical power supplied to each electrode ispreferably in the range of 90˜270°, and in particular, the oppositephase (i.e., 180°) is preferred.

In this operation, it is preferable to form the film while performingbias applying, such as high frequency bias or pulse D.C. bias, to thedisc D, using the electrical bias source 13.

The conditions of bias such as voltage and the like are preferably asdescribed in the aforementioned.

The formed carbon protective film contains a higher content ofdiamond-like-carbons (DLC), which exhibit an increased hardness.

In the method for manufacturing magnetic recording medium according tothe present embodiment, subsequently, the disc D formed with theaforementioned carbon protective film is transported into the chamber 74of the ultraviolet ray irradiation device, and the surface of the carbonprotective film of the aforementioned disc D is irradiated withultraviolet rays comprising a wavelength of preferably 100˜400 nm, usingthe ultraviolet ray source 75.

If the wavelength of the ultraviolet rays is less than 100 nm, energyloss becomes great, while if the wavelength exceeds 400 nm, the effectsof improving the properties of the carbon protective film 23 areinsufficient, and hence undesirable.

The preferred condition at the time of irradiating with ultraviolet raysis an illuminance of 5˜50 mW/cm², and radiation duration of 2˜600seconds.

Subsequently, the disc D which has passed through the ultraviolet raysirradiation device, is transported into the washing apparatus, andcleaning water supplied from the supply source 87 is injected at theaforementioned disc D, using a nozzle 88, to clean the surface of thecarbon protective film. As the cleaning water used herein, a ultrapurewater with only a small unpurified content is preferred due to itssuperior effectiveness in cleaning the surface of the carbon protectivefilm.

Subsequently, a lubricant such as perfluoropolyether, fomblin lubricant,and the like, is applied, according to a dipping method or the like, tothe carbon protective film on the surface of the disc D, which haspassed through the washing apparatus, to form a lubricating film. Inthis manner, a magnetic recording medium, wherein a non-magnetic basefilm, magnetic film, carbon protective film and lubricating film aresuccessively formed on a substrate, is obtained.

Examples of the magnetic recording medium manufactured according to theaforementioned manufacturing method may include a magnetic recordingmedium with a similar structure to that shown in FIG. 2.

In the magnetic recording medium of this example, a non-magneticsubstrate S, a non-magnetic base film 31, a magnetic film 32, a carbonprotective film 33, and a lubricating film 34 are provided.

In the aforementioned method for manufacturing a magnetic recordingmedium, since the surface of the carbon protective film 33 is irradiatedwith ultraviolet rays prior to forming the lubricating film 34, thequality of the film surface is improved, and the adhesion of the carbonprotective film 33 to the lubricating film 34 is increased, leading to asuperior durability.

The reason for the aforementioned magnetic recording medium exhibiting asuperior durability is attributed to the following. Specifically, by theirradiation with ultraviolet rays, the shallow area of the carbonprotective film 33, near the surface, contains a large amount ofdangling bonds, and bonding involving this dangling bonds of the carbonprotective film 33 firmly adheres to the lubricating film 34.

Accordingly, it is possible to make the carbon protective film thinner,and thereby reduce spacing loss. In addition, it is possible to preventproblems such as spin-off during CSS operation.

Thus, it is possible to provide a highly reliable magnetic recordingmedium, which is capable of increasing the recording density withoutlowering the output properties thereof.

Additionally, by means of using an excimer emission lamp as theultraviolet ray source 75, it is possible to obtain a high output usinga short pulse width, and thereby efficiently improve the quality of thecarbon protective film 33 surface.

In addition, by means of washing the surface of the carbon protectivefilm 33 with water, it is possible to remove the impurities that areattached to the surface of the carbon protective film 33, and therebyclean the film.

Thus, it is possible to prevent a reduction in the bonding strengthbetween the carbon protective film 33 and lubricating film 34 due toimpurities lying between the two films, which in turn prevents anyreduction in the durability of the magnetic recording medium.

In addition, in the manufacturing method according to the aforementionedembodiment, after forming the carbon protective film, the surface isirradiated with ultraviolet rays, and then washed using water. However,the method for manufacturing magnetic recording medium according to thepresent invention is not limited thereto, and the washing process mayprecede the process of irradiating with ultraviolet rays, after formingthe carbon protective film.

In addition, the surface of the carbon protective film may also bewashed using water without undergoing irradiation with ultraviolet rays.Furthermore, the surface of the carbon protective film may be irradiatedwith ultraviolet rays without being washed.

Additionally, in the method for manufacturing magnetic recording mediumaccording to the present invention, after forming the carbon protectivefilm, a tape-vanishing process, wherein micro-ridges on the surface ofthe carbon protective film are scraped off, may also be performed.

In the following, the effects of the present invention are specified,using concrete examples.

TEST EXAMPLE 68

A magnetic recording medium was manufactured, using a plasma CVDapparatus, an ultraviolet ray irradiation device, and a washingapparatus shown in FIGS. 1, 6, and 7, respectively, according to thefollowing process.

After an aluminium alloy substrate coated with a NiP metal film (with adiameter of 95 mm and thickness of 0.8 mm) was treated with mechanicaltexture-processing to form an average surface roughness of 20 Å, anon-magnetic base film 31 (with a thickness of 600 Å) comprising a Cralloy, and a magnetic film 32 comprising a Co alloy (Co_(82Cr) ₁₅Ta₃)were successively formed on both sides of the substrate S, using aspattering device (3010 manufactured by Anelva), to obtain a disc D.

Subsequently, the disc D was transported into the chamber 10 of theplasma CVD apparatus, and a mixed gas was supplied from the supplysource 14 into the chamber to achieve a flow rate of 130 sccm.

A mixed gas of toluene and hydrogen, with a mixing ratio of toluene tohydrogen of 1 to 12 by volume, was used as the reactant gas.Additionally, the inner pressure of the chamber 10 was maintained at 6Pa.

At the same time, high frequency electrical power of 450 W was suppliedto the electrodes 11 to generate plasma, while applying pulse D.C. biasof −120V (with a frequency of 200 kHz and pulse width of 500 ns) to thedisc, using the electrical bias source 13, to form a carbon protectivefilm 33 with a thickness of 50 Å on both sides of the disc D. Thetemperature of the disc D, and coating rate were maintained at 130° C.,and 450 Å/min, respectively. The difference in the phase of highfrequency electrical power supplied to each electrode 11 was set at180°. In addition, the distance between the disc D and electrode 11 wasset at 30 mm.

Subsequently, the disc D wherein the carbon protective film was formedaccording to the aforementioned operation was transported into thewashing apparatus, wherein the surface was washed using ultrapure water.

The disc D was then transported into the chamber 74, where the disc Dwas irradiated with ultraviolet rays, using the ultraviolet ray source75.

Herein, an excimer lamp (manufactured by Ushio Denki), which is able toirradiate ultraviolet rays of a wavelength of 172 mm (with a half bandwidth of 14 nm), was used as the ultraviolet ray source 75, andultraviolet ray irradiation was performed for 30 seconds at anilluminance of 10 mW/cm² under a nitrogen gas atmosphere.

Subsequently, the disc D was washed in the washing apparatus again, andthen a fomblin lubricant (Fomblin Zdol 2000) was applied 33 afterwashing to the carbon protective film, according to a dipping method. Alubricating film 34 with a thickness of 20 Å was then formed, to obtaina magnetic recording medium.

TEST EXAMPLE 69

A magnetic recording medium was manufactured in the same manner as inTest Example 68, with the exception that an excimer lamp (manufacturedby Ushio Denki) capable of irradiating ultraviolet rays with awavelength of 222 nm (with a half band width of 2 nm) was used as theultraviolet ray source 75, and the disc D was irradiated withultraviolet rays for 30 seconds at an illuminance of 7 mW/cm² under anitrogen gas atmosphere.

TEST EXAMPLE 70

A magnetic recording medium was manufactured in the same manner as inTest Example 68, with the exception that the disc D was irradiated withultraviolet rays under ambient air.

TEST EXAMPLE 71

A magnetic recording medium was manufactured in the same manner as inTest Example 68, with the exception that the disc D was not washed inthe washing apparatus. In this test, ultraviolet ray source 75 used inTest Example 68 was used.

TEST EXAMPLE 72

A magnetic recording medium was manufactured in the same manner as inTest Example 68 except that irradiation with ultraviolet rays was notperformed.

The bonded ratio test, spin-of test and CSS test described in thefollowing were performed on each magnetic recording medium, obtained ineach of the aforementioned

TEST EXAMPLES

(1) Bonded Ratio Test

Each of the aforementioned magnetic recording medium was soaked in asolvent (AK225 manufactured by Asahi Glass) for 15 minutes, and thenremoved. The ratio of the thickness of the lubricating film 34 prior tothis operation and after this operation was then calculated inpercentage. The thickness of the lubricating film 34 was measured at theposition where the radius measured 20 mm, using ESCA.

(3) Spin-off Test

The aforementioned magnetic recording medium was rotated at a rotationalspeed of 10000 rpm and a temperature of 100° C. for 168 hours. The ratioof the thickness of the lubricating film 34 prior to this operation andafter this operation was then calculated in percentage. The thickness ofthe lubricating film 34 was measured at the positions, where the radiusof the magnetic recording medium measured 20 mm (inner circumference)and 42 mm (outer circumference), respectively, using FT-IR.

(3) CSS Test

Using an MR head, a CSS operation was performed on the aforementionedmagnetic recording medium 5000 times, at a rotational speed of 7200 rpm,and a low temperature of 5° C. with a low humidity of 15%.

In this CSS test, two types of tests were performed: in one test, theaforementioned magnetic recording medium was baked at a temperature of180° C. for 3 hours prior to the aforementioned CSS operation, and inthe other, no such baking process was performed. The test results areshown in Table 11.

TEST EXAMPLE 73

A magnetic recording medium was manufactured in the same manner as inTest Example 68 with the exception that neither irradiation usingultraviolet rays nor washing was performed.

TEST EXAMPLE 74

A magnetic recording medium was manufactured in the same manner as inTest Example 68 with the exception that the carbon protective film witha thickness of 100 Å was formed according to a conventionally known,spattering method.

TEST EXAMPLE 75

A magnetic recording medium was manufactured in the same manner as inTest Example 74 with the exception that washing was not performed.

TEST EXAMPLE 76

A magnetic recording medium was manufactured in the same manner as inTest Example 74 with the exception that irradiation with ultravioletrays was not performed.

TEST EXAMPLE 77

A magnetic recording medium was manufactured in the same manner as inTest Example 74 with the exception that neither irradiation usingultraviolet rays nor washing was performed.

The aforementioned three types of tests were performed on each of theaforementioned magnetic recording media. The test results are shown inTable 11.

In the table, the plasma CVD method is referred to as “pCVD method”, andultraviolet ray irradiation is referred to as “UV irradiation”.

TABLE 11 Carbon Spin-off Spin-off protective UV Inner Outer CSS filmirradia- Wash- Bonded circum- circum- w/o With coating tion ing ratioference ference baking baking method source process (%) (%) (%) processprocess Test pCVD Excimer with 33 74 80 No crash No crash Example 68method lamp Test pCVD Excimer with 51 82 89 No crash No crash Example 69method lamp Test pCVD Excimer with 39 77 83 No crash No crash Example 70method lamp Test pCVD Excimer without 31 72 79 No crash No crash Example71 method lamp Test pCVD — with 15. 42 49 No crash No crash Example 72method Test pCVD — without 11 38 44 No crash Crash Example 73 methodTest Spattering Excimer with 56 84 92 Crash Crash Example 74 method lampTest Spattering Excimer without 53 82 89 Crash Crash Example 75 methodlamp Test Spattering — with 30 75 82 Crash Crash Example 76 method TestSpattering — without 28 76 82 Crash Crash Example 77 method

From the results of CSS shown in Table 11, it is clear that the magneticrecording media, manufactured according to a method in which the carbonprotective film was formed according to the plasma CVD method, andultraviolet ray irradiation and/or washing with ultrapure water wasperformed prior to lubricating the film, exhibited sufficient durabilityagainst CSS operations performed 5000 times.

Additionally, from the results of the bonded ratio test and spin-offtest, the magnetic recording media, manufactured according a the methodin which UV irradiation was performed, exhibited a lower reduction ratein thickness of the lubricating film, compared to those manufacturedaccording to a method in which UV irradiation was not performed.

As explained in the aforementioned, according to the present invention,it is possible to form a carbon protective film of a superiordurability. As a result, it is also possible to make the carbonprotective film thinner while also maintaining a sufficient durability,and thereby reduce spacing loss.

Consequently, it is possible to provide a highly reliable magneticrecording medium which is capable of sufficiently increasing therecording density without lowering the output properties thereof.

In the following, another embodiment of the magnetic recording mediumaccording to the present invention is described.

The magnetic recording medium according to the present embodimentcomprises a structure similar to that shown in FIG. 2. In the magneticrecording medium according to the present embodiment, a non-magneticsubstrate S, a non-magnetic base film 31, a magnetic film 32, a carbonprotective film 33, and a lubricating film 34 are provided.

Examples of the non-magnetic substrate S may include an aluminium alloysubstrate coated with a NiP metal film, in addition to substratescomprising glass, silicone, and the like.

The surface of the substrate S is preferably treated withtexture-processing such as mechanical texture-processing. In particular,the average surface roughness (Ra) is preferably in the range of 1˜20 Å.

The material and thickness of the non-magnetic base film 31 and magneticfilm 32 are as described in the aforementioned. The thickness of thenon-magnetic base film 31 and magnetic film 32 are preferably in therange of 50˜1000 Å, and 50˜800 Å, respectively.

The carbon protective film 33 is formed according to the plasma CVDmethod.

The thickness of the carbon protective film is preferably in the rangeof 30˜100 Å.

In the magnetic recording medium according to the present embodiment,the lubricating film 34 principally comprises at least one compoundselected from among the compounds represented by the following formula(1) through (5), number average molecular weight of which fall in therange of 500˜6000. The thickness of the lubricating film 34 ispreferably in the range of 5˜40 Å.

In this specification, the term “principally comprise” signifies thatthe particular component is contained in an amount greater than 70 wt %.

 F—(CF₂CF₂CF₂O)_(p)—CF₂CF₂—COOCH₂CH₂—O—C₆H₅  (2)

F—(CF₂CF₂CF₂O)_(q)—CF₂CF₂CH₂—OH  (3)

HOCH₂—CF₂O—(C₂F₄O)_(r)—(CF₂O)_(s)—CF₂—CH₂OH  (4)

HO—(CH₂CH₂—O)_(t)—CH₂CF₂O—(CF₂CF₂O)_(u)—(CF₂O)_(v)—CF₂CH₂—(OCH₂CH₂)_(w)—OH  (5)

[wherein, m, n, p, q, r, s, t, u, v, and w represent an integer,respectively].

If the molecular weight of the compounds represented by theaforementioned formula (1) through (5) is less than 500, “spin-off”worsens. On the other hand, if the molecular weight of the compoundsexceeds 6000, the lubricating ability of the surface of the resultantmagnetic recording medium deteriorates, undesirably leading to aninferior CSS property.

Among the aforementioned, compounds represented by the formula (1) or(5), with a number average molecular weight of 500˜6000, are especiallypreferred as the principal component of the lubricating film 34, sincethese compound improve the spin-off properties and CSS characteristics.

Additionally, the lubricating film 34 may principally comprise amixture, wherein a compound represented by the following formula (6) ismixed into at least one compound selected from among the aforementionedformula (1) through (5), having a number average molecular weight is500˜6000, at a mixing ratio of 0.1˜20 wt %.

[wherein, x represents an integer between 0˜6].

The formula (6) represents a compound, wherein six units of thestructure represented by (F—C₆H₄—O) and/or (O—C₆H₄—CF₃) are bonded to atleast one selected from among a nitrogen and/or phosphorus which havesix-member-ring structure.

When using the compound represented by the formula (6), if theproportional content of this compound is less than 0.1 wt %, thelubricating ability of the surface of the resultant magnetic recordingmedium deteriorates, leading to an inferior CSS property. When theproportional content of the aforementioned exceeds 20 wt %, smearsderived from this compound tend to stick to the head, which isundesirable.

In the following, the method for manufacturing the aforementionedmagnetic recording medium is described.

In order to manufacture the aforementioned magnetic recording medium,initially, a non-magnetic base film 31 and magnetic film 32 were formedon both sides of a non-magnetic substrate, according to a method such asa spatter-coating method, or the like, to obtain a disc D.

Subsequently, the disc D is transported into the chamber 10 of theaforementioned plasma CVD apparatus, and the surface of the disc D isexposed to a reactant gas, which is supplied from the supply source 14through the introduction tube 15 into the chamber 10, from which the gasis exhausted via the exhaust tube 16 to circulate the gas within.

The reactant gas is a mixed gas of hydrocarbon and hydrogen, with amixing ratio of hydrocarbon to hydrogen in the range of 2 to 1˜1 to 100by volume. The hydrocarbon preferably comprises at least one type ofhydrocarbon selected from among lower saturated hydrocarbons, lowerunsaturated hydrocarbons, and lower cyclic hydrocarbons.

In this operation, the flow rate of the reactant gas is preferably inthe range of 50 ˜500 sccm. Additionally, the inner pressure of thechamber 10 is preferably maintained at a predetermined value, such as0.1˜10 Pa.

At the same time, using the high frequency electrical power source 12,high frequency electrical power of preferably 50˜2000 W is supplied tothe electrodes 11 to generate plasma, and a carbon protective film 33with a thickness of preferably in the range of 30˜100 Å, is formed onboth sides of the disc D by means of plasma chemical gas phase growth,using the aforementioned reactant gas as a starting material.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode 11 different. By means of making the phases of electricalpower supplied to each electrode 11 different, it is possible to improvethe coating rate and durability of the protective film. The differencein the phase of electrical power supplied to each electrode ispreferably in the range of 90 ˜270°, and in particular, the oppositephase (i.e., 180°) preferred.

In this operation, it is preferable to form the film while performingbias applying, such as high frequency bias or pulse D.C. bias, to thedisc D, using the electrical bias source 13.

The conditions of bias such as voltage and the like are preferably asdescribed in the aforementioned.

The resultant carbon protective film 33 contains a higher content ofdiamond-like-carbons (DLC), which exhibit an increased hardness.

Subsequently, the lubricant comprising the compounds represented by theaforementioned chemical formula is applied to the carbon protective film33, according to a dipping method or the like, to form a lubricatingfilm 34 with a thickness of preferably 5˜40 Å. In this manner, amagnetic recording medium is obtained, in which the non-magnetic basefilm 31, magnetic film 32, carbon protective film 33, and lubricatingfilm 34 were successively formed on a substrate S.

According to the aforementioned magnetic recording medium, wherein thelubricating film 34 principally comprises at least one compound selectedfrom among the compounds represented by formula (1) through (5), oralternatively principally comprises a mixture of the aforementionedcompound and a compound represented by formula (6), in which theproportional content of the compound represented by the formula (6) is0.1˜20 wt %, the aforementioned lubricating film 34 exhibits a greateradhesion to the carbon protective film 33, and hence provides for asuperior durability.

The reason for the aforementioned magnetic recording medium exhibiting asuperior durability is attributed to the fact that the lubricating filmcomprising the aforementioned components is firmly adhered to the carbonprotective film 33 formed according to the plasma CVD method.

As a result, it is possible to make the carbon protective film 33thinner while also maintaining a sufficient durability, and therebyreduce spacing loss. Additionally, there are no problems such asspin-off in CSS operation.

Consequently, it is possible to provide a highly reliable magneticrecording medium, which is capable of sufficiently increasing therecording density without lowering the output properties thereof.

In the following, the effects of the present invention are specifiedusing concrete examples.

TEST EXAMPLES 78˜84

The magnetic recording medium similar to that shown in FIG. 2 wasmanufactured as follows.

After an aluminium alloy substrate coated with a NiP metal film (with adiameter of 95 mm and thickness of 0.8 mm) was treated with mechanicaltexture-processing to form an average surface roughness of 20 Å, anon-magnetic base film 31 (with a thickness of 600 Å) comprising a Cralloy, and a magnetic film 32 comprising a Co alloy (Co₈₂Cr₁₅Ta₃) weresuccessively formed on both sides of the substrate S, using a spatteringdevice (3010 manufactured by Anelva), to obtain a disc D.

Subsequently, the disc D was transported into the chamber 10 of theplasma CVD apparatus, and a mixed gas was supplied from the supplysource 14 into the chamber 10 to achieve a flow rate of 130 sccm.

A mixed gas of toluene and hydrogen, with a mixing ratio of toluene tohydrogen of 1 to 12 by volume, was used as the reactant gas.Additionally, the inner pressure of the chamber 10 was maintained at 6Pa.

At the same time, high frequency electrical power of 450 W was suppliedto the electrodes 11 to generate plasma, while applying pulse D.C. biasof −120V (with a frequency of 200 kHz and pulse width of 500 ns) to thedisc, using the electrical bias source 13, to form a carbon protectivefilm 33 with a thickness of 50 Å on both sides of the disc D. Thetemperature of the disc D, and coating rate were maintained at 130° C.,and 450 Å/min, respectively. The difference in the phase of highfrequency electrical power supplied to each electrode 11 was set at180°. In addition, the distance between the disc D and electrode 11 wasset at 30 mm.

Subsequently, a lubricating film 34 with a thickness of 20 Å, comprisingthe materials shown in Table 12, was formed on the carbon protectivefilm 33, according to a dipping method, to obtain a magnetic recordingmedium.

In the table, the numbers in parenthesis correspond to the number of theaforementioned formula. That is, for example, Fomblin ZTETRAOL 2000 (1)used in Test Example 78 comprises the compound represented by theaforementioned formula (1).

Additionally, in the magnetic recording medium in Test Example 83, thelubricating film 34 comprises a mixture of Fomblin ZTETRAOL 2000 (1) andFomblin Zdol 2000 (4) (with a mixing ratio of 1 to 1 by volume).

Additionally, in the magnetic recording medium in Test Example 84, thelubricating film 34 comprises the material in which X1P (6) was added toDemnum SP (2) at 3 wt %.

The bonded ratio test, and CSS test described in the following wereperformed on the resultant magnetic recording media.

(1) Bonded Ratio Test

The aforementioned magnetic recording medium was soaked in a solvent(AK225 manufactured by Asahi Glass) for 15 minutes, and then removed.The ratio of the thickness of the lubricating film 34 prior to thisoperation and after this operation was then calculated in percentage.The thickness of the lubricating film 34 was measured at the positionwhere the radius measured 20 mm, using ESCA.

In addition, after the aforementioned bonded ratio test, the magneticrecording medium was left under the environment of a temperature of 120°C. for 3 hours, after which the bonded ratio test was performed in thesame manner. The test results are shown in Table 12.

In Table 12, the test results after thermal treatment at 120° C. areshown in the column of ‘with baking’, and the test results beforethermal treatment are shown in the column of ‘without baking’.

(2) CSS Test

After the aforementioned magnetic recording medium was baked at atemperature of 120° C. for 3 hours, a CSS operation was performed, usingan MR head, on the aforementioned magnetic recording medium 10000 timesat a rotational speed of 7200 rpm, and a low temperature of 5° C. with alow humidity of 15%. The coefficient of dynamic friction on the surfaceof the magnetic recording medium was subsequently measured. Furthermore,after the aforementioned magnetic recording medium was allowed to sitfor 6 hours, the coefficient of static friction was measured.

TEST EXAMPLES 85˜88

A magnetic recording medium was manufactured, wherein the carbonprotective film was formed according to the spattering method, and thelubricating film comprised the materials shown in Table 12.

The aforementioned two types of tests were performed on these magneticrecording media. The test results are shown in Table 12.

In the table, plasma CVD method is expressed as “pCVD” method.

TABLE 12 Bonded ratio Coefficient Carbon Material for without withCoefficient of static protective film lubricating baking baking ofdynamic friction coating method film (%) (%) friction (−) (gram) TestPCVD method Fomblin 38 73 0.85 2.3 Example 78 ZTETRAOL 2000 (1) TestPCVD method Demnum SP 10 33 1.41 3.8 Example 79 (2) Test PCVD methodDemnum SA 11 42 1.27 3.3 Example 80 (3) Test PCVD method Fomblin Zdol 1558 0.90 2.2 Example 81 2000 (4) Test pCVD method Fomblin TX 33 69 0.881.8 Example 82 (5) Test pCVD method Fomblin 32 67 0.79 1.8 Example 83ZTETRAOL 2000 (1) + Fomblin Zdol 2000 (4) Test pCVD method Demnum SP 1032 0.59 2.5 Example 84 (2) + X1P (6) Test Spattering Fomblin 55 93 CrashCrash Example 85 method ZTETRAOL 2000 (1) Test Spattering Demnum SP 2545 1.73 6.3 Example 86 method (2) Test Spattering Fomblin Zdol 32 91Crash Crash Example 87 method 2000 (4) Test Spattering Demnum SP 23 420.87 4.1 Example 88 method (2) + X1P (6)

From the results of the CSS test shown in Table 12, it is clear that themagnetic recording media, in which the carbon protective film was formedaccording to the plasma CVD method, and the lubricating film principallycomprised at least one compound selected from among the formula (1)through (5), or the aforementioned compound, into which a compoundrepresented by the formula (6) is mixed in at 0.1˜20 wt %, maintained asmall coefficient of dynamic friction, and exhibited a desirableresistance to sliding.

Accordingly, the aforementioned magnetic recording medium exhibited asuperior durability.

Additionally, the magnetic recording medium, wherein the carbonprotective film was formed according to the spattering method, induced ahead crash or exhibited an increased coefficient of static friction,from baking process at a high temperature. Whereas the magneticrecording medium, wherein the carbon protective film was formedaccording to the plasma CVD method, and the lubricating film principallycomprised the aforementioned compound(s), maintained a small coefficientof dynamic friction even after treatment at a high temperature.

As explained in the aforementioned, according to the present invention,it is possible to form a carbon protective film with a superiordurability. As a result, it is also possible to make the carbonprotective film thinner while also maintaining a sufficient durability,and thereby reduce spacing loss.

Therefore, it is possible to provide a highly reliable magneticrecording medium, which is capable of sufficiently increasing therecording density without lowering the output properties thereof.

FIG. 8 shows another embodiment of the magnetic recording mediumaccording to the present invention. In the magnetic recording mediumshown herein, a non-magnetic base film 61, magnetic film 62, and carbonprotective film 63 are successively formed on a non-magnetic substrateS.

Examples of the non-magnetic substrate S may include an aluminium alloysubstrate coated with a NiP metal film, and substrates comprising glass,silicone, and the like.

In addition, the surface of the substrate S is preferably treated withtexture-processing such as mechanical texture-processing. In particular,the average surface roughness (Ra) is preferably in the range of 1˜20 Å.

The material of the non-magnetic base film 61 and magnetic film 62 areas described in the aforementioned. The thickness of the non-magneticbase film 61 and magnetic film 62 are preferably in the range of 50˜1000Å, and 50˜800 Å, respectively.

The carbon protective film 63 is formed according to the plasma CVDmethod, and Co extraction amount to the substrate area is 3 ng/cm² orless, preferably 2ng/cm² or less, or more preferably 1.5 ng/cm² or less.

Herein, the Co extraction amount represents the amount of Co extractedfrom water, at the time when the magnetic recording medium, wherein aprotective film is formed on the magnetic film containing Co at 50 at %or greater, is left for 96 hours at a temperature of 60° C. and ahumidity of 80%, and then soaked in the water at 20° C. for 30 minutes.

If this Co extraction amount exceeds 3 ng/cm², the durability of themagnetic recording medium tends to weaken, which is undesirable.

The thickness of the carbon protective film 63 is preferably in therange of 30˜100 Å.

If the thickness is less than 30 Å, the strength of the carbonprotective film 63 is inadequate, and if the thickness exceeds 100 Å,the resultant magnetic recording medium exhibits greater spacing loss atthe time of recording and replay, leading to a likelihood of loweringthe output properties at the time of increasing the recording density.

Additionally, a lubricating film with a thickness of 5˜40 Å, comprisingperfluoropolyether, fomblin lubricant, or the like, may be provided onthe carbon protective film 63.

In the following, the method for manufacturing the aforementionedmagnetic recording medium is described.

When manufacturing the aforementioned magnetic recording medium, theplasma CVD apparatus shown in FIG. 1 may be used.

In order to manufacture the aforementioned magnetic recording medium,using this equipment, initially, a non-magnetic base film 61 comprisinga Cr alloy or the like, and a magnetic film 62 comprising a Co alloy andthe like are successively formed on both sides of a non-magneticsubstrate S, comprising aluminium alloy coated with a NiP metal film,according to a method such as the spatter-coating method, and the like,to obtain a disc D.

Subsequently, the disc D is transported into the chamber 10 of theaforementioned plasma CVD apparatus, and the surface of the disc D isexposed to a reactant gas, which is supplied from the supply source 14through the introduction tube 15 into the chamber 10, from which the gasis exhausted via the exhaust tube 16 to circulate the gas within.

The reactant gas is a mixed gas of hydrocarbon and hydrogen, with amixing ratio of hydrocarbon to hydrogen in the range of 2 to 1˜1 to 100by volume. The hydrocarbon preferably comprises at least one type ofhydrocarbon selected from among lower saturated hydrocarbons, lowerunsaturated hydrocarbons, and lower cyclic hydrocarbons.

In this operation, the flow rate of the reactant gas is preferably inthe range of 50˜500 sccm. Additionally, the inner pressure of thechamber 10 is preferably maintained at a predetermined value, such as0.1˜10 Pa.

At the same time, using the high frequency electrical power source 12,high frequency electrical power of preferably 50˜2000 W is supplied tothe electrodes 11 to generate plasma, and a carbon protective film 63with a thickness of preferably in the range of 30˜100 Å, is formed onboth sides of the disc D by means of plasma chemical gas phase growth,using the aforementioned reactant gas as a starting material.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode 11 different. By means of making the phases of electricalpower supplied to each electrode 11 different, it is possible to improvethe coating rate and durability of the protective film. The differencein the phase of electrical power supplied to each electrode ispreferably in the range of 90˜270°, and in particular, more preferablyopposite phase (i.e., 180°).

In this operation, it is preferable to form the film while performingbias applying, such as high frequency bias or pulse D.C. bias, to thedisc D, using the electrical bias source 13.

The conditions of bias such as voltage and the like are preferably asdescribed in the aforementioned.

The formed carbon protective film 63 contains a higher content ofdiamond-like carbon (DLC), which exhibit an increased hardness, higherdensity and greater strength, wherein the Co extraction amount withrespect to the substrate area is 3 ng/cm² or less.

Subsequently, a lubricating film is preferably formed on the carbonprotective film 63 according to a dipping method, or the like, by meansof applying a lubricant such as perfluoropolyether, fomblin lubricant,and the like.

The aforementioned magnetic recording medium, wherein a carbonprotective film 63 is formed according to the plasma CVD method, and theCo extraction amount to substrate area is 3 ng/cm2 or less, exhibits anincreased hardness and higher density, in addition to displayingsuperior strength and resistance to corrosion.

Accordingly, it is possible to make the carbon protective film 63thinner while also maintaining a sufficient durability, and therebyreduce spacing loss.

Therefore, it is possible to provide a highly reliable magneticrecording medium, which is capable of sufficiently increasing therecording density without lowering the output properties thereof.

In the following, the effects of the present invention are specified,using concrete examples.

TEST EXAMPLES 89˜92

The magnetic recording medium shown in FIG. 8 is manufactured asfollows.

After an aluminium alloy substrate coated with a NiP metal film (with adiameter of 95 mm and thickness of 0.8 mm) was treated with mechanicaltexture-processing to form an average surface roughness of 20 Å, anon-magnetic base film 61 (with a thickness of 600 Å) comprising a Cralloy, and a magnetic film 62 comprising a Co alloy (Co₈₂Cr₁₅Ta₃) weresuccessively formed on both sides of the substrate S, using a spatteringdevice (3010 manufactured by Anelva), to obtain a disc D.

Subsequently, the disc D was transported into the chamber 10 of theplasma CVD apparatus, and a reactant gas was supplied from a supplysource 14 into the chamber. A mixed gas comprising toluene and hydrogenwas used as the reactant gas. The flow rate of each was as shown inTable 13. Additionally, the inner pressure of the chamber 10 wasmaintained at 6 Pa.

At the same time, high frequency electrical was supplied to theelectrodes 11, power under the conditions shown in Table 13, to generateplasma, and a carbon protective film 63 with a thickness of 50 Å wasformed on both sides of the disc D, to yield a magnetic recordingmedium.

At this time, pulse D.C. bias (DC) or high frequency bias (RF) wasapplied to the disc D, under the conditions shown in Table 13, using abias electrical source 13. Additionally, the temperature of the disc Dat the time of coating the film was set at 130° C. In addition, thedifference of the phase of high frequency electrical power supplied toeach electrode 11 was set at 180°. Additionally, the distance betweenthe disc D and electrodes 11 were set at 30 mm. In the table, plasma RFelectrical power represents the high frequency electrical power suppliedto the electrodes 11.

The Co extraction amount of the magnetic recording medium onto which theaforementioned carbon protective film 63 is formed, was measuredaccording to the corrosion test described in the following.

The test comprised the steps of allowing the aforementioned magneticrecording medium to sit for 96 hours at a high temperature (60° C.) andhigh humidity (80%); subsequently soaking the medium in 50 cc ofultrapure water for 30 minutes; and then measuring the amount of Coextracted in the pure water. Additionally, another test was alsoperformed in the same manner with the exception that the aforementionedmagnetic recording medium was instead allowed to sit at a normaltemperature (25° C.) and normal humidity (50%) for 96 hours. The testresults are shown in Table 14.

The results of Raman spectral analysis (argon ion laser excitation),performed on the aforementioned magnetic recording medium, using a Ramanspectral analysis apparatus (manufactured by JEOL), are also shown inTable 14.

Additionally, the hardness of the carbon protective film 63 of theaforementioned magnetic recording medium was measured using apico-indentor (manufactured by Hysitron). These results are also shownin Table 14.

TEST EXAMPLE 93

A magnetic recording medium, in which a carbon protective filmcomprising carbon was formed according to the conventionally known,spatter-coating method, using a target comprising carbon, wasmanufactured.

At this time, argon (Ar) was used as the spatter gas, and its flow ratewas set at 90 sccm.

TEST EXAMPLE 94

A carbon protective film was formed according to the conventionallyknown, spatter-coating method, using a target comprising carbon. At thistime, a mixed gas of Ar and nitrogen was used as the spatter gas, andtheir flow rates were set at 100 sccm, and 50 sccm, respectively.Accordingly, the protective film comprised nitrogen and carbon.

The above-described corrosion test and Raman spectral analysis wereperformed on each magnetic recording medium. In addition, the hardnessof each magnetic recording medium was measured. The results are shown inTable 14.

TABLE 13 Protective Reactant gas Bias conditions film Hydro- Plasma RFPulse Voltage/ coating Toluene gen electrical Frequency width electricalmethod (sccm) (sccm) power (W) Type (kHz) (ns) power Test pCVD 10 240300 DC 200 500 −100 V Example 89 method Test pCVD 10 120 500 RF 400 — 50W Example 90 method Test pCVD 10 120 500 DC 200 500 −100 V Example 91method Test pCVD 10 120 500 RF 400 — 30 W Example 92 method TestSpattering — — — — — — — Example 93 method Test Spattering — — — — — — —Example 94 method

TABLE 14 Co Co extraction extraction amount amount Raman spectralanalysis Coating (60° C., 80%) (25° C., 50%) ∪G-line Hardness rate(ng/cm²) (ng/cm²) (cm⁻¹) Id/Ig (Gpa) (Å/min) Test 0.76 0.38 1543.8 0.5526.6 458 Example 89 Test 0.53 0.38 1556.2 0.90 24.7 409 Example 90 Test1.21 0.49 1541.9 0.66 20.5 753 Example 91 Test 1.47 0.55 1532.2 0.5019.8 789 Example 92 Test 3.39 1.04 1572.3 4.14 10.3 — Example 93 Test4.47 1.19 1561.8 2.95 11.8 — Example 94

From Tables 13 and 14, the magnetic recording media, in which a carbonprotective film was formed according to the plasma CVD method, andwherein the Co extraction amount to substrate area (at 60° C. and 80%humidity) was 3 ng/cm2 or less, showed a G-band peak at a higherfrequency, exhibited a smaller Id/Ig, and displayed an increasedhardness due to the effects of DLC, compared to the other magneticrecording media.

As explained in the aforementioned, according to the present invention,it is possible to form a carbon protective film with a superiordurability. As a result, it is possible to make the carbon protectivefilm thinner while also maintaining a sufficient durability, and therebyreduce spacing loss.

Therefore, it is possible to provide a highly reliable magneticrecording medium, which is capable of sufficiently increasing therecording density without lowering the output properties thereof.

FIG. 9 shows the texture-processing equipment used in another embodimentof the method for manufacturing magnetic recording medium according tothe present invention.

The texture-processing equipment shown herein is provided with asubstrate support member 24, which supports the non-magnetic substrate Sfor texture-processing in a manner such that it can rotate; abrasivetape supply members 25 and 25, which supply abrasive tape A tomechanically scrape the non-magnetic substrate S; contact rollers 26 and26, which press the abrasive tape A against one area of the surface ofthe substrate S; and abrasive particle supply nozzles 27 and 27 whichsupply abrasive particles to the area of contact between the abrasivetape A and substrate S.

The abrasive tape supply member 25 is provided with a delivery roll 25a, which sends the abrasive tape A out, and a receiving roll 25 b, whichreceives the abrasive tape A. The aforementioned supply member 25comprises a structure in which the abrasive tape A, wound arounddelivery roll 25 a, may be received by receiving roll 25 b, at any speedin the direction perpendicular to the radial direction of the substrateS, where the abrasive tape A is in contact with the substrate S. Anabrasive tape supply member 25 is provided on each side of the substrateS.

Additionally, the abrasive tape supply member 25 is preferably designedsuch that the abrasive tape A is able to oscillate in a directionapproximately perpendicular to the running direction of the tape.

In addition, it is possible to design the aforementioned substratesupport member 24 such that it is able to oscillate in a directionapproximately perpendicular to the running direction of the tape, inorder so that the substrate S is able to oscillate against the abrasivetape A.

The contact rollers 26 may comprise a synthetic resin, rubber, metal,and the like, and are provided on each side of the substrate S, suchthat the roller 26 lies in contact with the substrate S, via theabrasive tape A, in a direction approximately perpendicular to therunning direction of the tape.

The outer diameter of the contact roller 26 is preferably in the rangeof 20˜100 mm, and the length in the axial direction is preferably set ata length which reaches the most-outer circumference from the most-innercircumference on the surface of the substrate S to undergo abrasion atthe time of texture-processing.

The contact roller 26 is preferably attached in the direction of thesubstrate S such that the aforementioned abrasive tape is pushed againstthe substrate S with a predetermined pressure such as 0.3˜4 kg/cm².

Examples of the abrasive tape A may include conventionally used,polishing tape, texture tape, and wiping tape; in particular, tapes witha thickness of 0.1˜1.0 mm and width of 20˜60 mm are preferred.

The abrasive supply nozzle 27 is provided at the upper portion of thecontact roller 26 such that abrasive particle slurry in the abrasiveparticle slurry tank (not shown) can be introduced to the area ofcontact between the abrasive tape A and substrate S.

In the following, another embodiment of the aforementioned method formanufacturing magnetic recording medium according to the presentinvention is described, using an example in which the aforementionedtexture-processing equipment and plasma CVD apparatus shown in FIG. 1are employed.

Initially, the non-magnetic substrate S is supported by a substratesupport member 24 of the texture-processing equipment.

The non-magnetic substrate may comprise any substrate that is generallyused as a substrate for magnetic recording medium, examples of which mayinclude an aluminium alloy substrate coated with a NiP metal film, andsubstrates comprising glass, silicone, and the like.

The substrate S is rotated in the direction shown by the arrow in thefigure at a predetermined speed.

The rotational speed of the substrate S is preferably in the range of300˜2000 rpm. A rotational speed less than 300 rpm results in areduction in the efficiency of texture-processing, while a rotationalspeed exceeding 2000 rpm tends to result in a non-uniform, processedsurface for the substrate.

The abrasive tape A set in the abrasive tape supply member 25 isreceived by means of the receiving roll 25 b. The speed at which theabrasive tape A is received preferably lies in the range of 0.1˜2cm/sec.

The abrasive tape A runs over the substrate S while in contact with bothsides of the substrate S, at the time of passing between the contactroller 26 and substrate S.

At the same time, an abrasive particle slurry stored in the abrasiveparticle slurry tank (not shown) is introduced and allowed to run ontothe abrasive tape A, via the abrasive particle supply nozzle 27.

The aforementioned abrasive particle slurry comprises a slurry in whichabrasive particles are suspended in water.

The abrasive particle may comprise any particle that is conventionallyused in texture-processing, examples of which may include diamondabrasive particles, alumina abrasive particles, carbon silicon, abrasiveparticles, and the like. Among the aforementioned, diamond abrasiveparticles are particularly preferred. The average particle diameter ispreferably in the range of 0.1˜0.5 μm.

If the average particle diameter is less than 0.1 μm, the resultantabrasion tends to be inadequate, while an average diameter exceeding 0.5μm tends to result in the surface of the substrate becoming too rough,both of which are undesirable.

As the abrasive particle slurry, the aforementioned abrasive particlesare preferably added to water to comprise approximately 5˜30%. Inaddition, the flow rate of the abrasive particle slurry is preferably inthe range of 10˜100 ml/min.

The abrasive particle slurry introduced from the abrasive particlesupply nozzle 27 reaches the area of contact between the abrasive tape Aand substrate S. Here, the abrasive particles in the abrasive particleslurry are rubbed onto the substrate S, by means of running the abrasivetape A in the direction perpendicular to the radial direction of thesubstrate S, to scrape the surface of the substrate S. By means ofscraping the surface of the rotating substrate S with abrasiveparticles, the resultant grooves are formed on the surface of thesubstrate in the running direction of the abrasive tape A, i.e.,approximately, along the periphery of the substrate S.

In the method for manufacturing magnetic recording medium according tothe present embodiment, the aforementioned operation is continued untilthe average surface roughness of the substrate S (Ra) becomes 1˜20 Å. Ifthe average surface roughness of the substrate S (Ra) is less than 1 Å,the resultant magnetic recording medium becomes excessively flat,leading to an inferior CSS property. If it exceeds 20 Å, the surface ofthe resultant magnetic recording medium becomes too irregular, leadingto a deterioration in the glide avalanche property.

In addition, when performing texture-processing, it is preferable tooscillate the abrasive tape A in the direction perpendicular to therunning direction of the tape by means of the aforementioned oscillationmechanism, to treat the processing surface of the substrate S uniformlyin the radial direction of the substrate. The frequency of oscillationis preferably in the range of 0.1˜5 Hz.

In addition, the width of the abrasive tape A at the time of oscillationis preferably in the range of 0.1˜30 mm.

Furthermore, the direction of oscillation of the abrasive tape A is notlimited to a direction perpendicular to the running direction of thetape, so long as the direction crosses the running direction of thetape.

Subsequently, using conventional spatter equipment or the like, anon-magnetic base film and magnetic film are formed on a substrate S,which has been treated with texture-processing, to obtain a disc D. Thematerial and thickness of the non-magnetic base film and magnetic filmare as described in the aforementioned.

The formation of the aforementioned non-magnetic base film and magneticfilm is not limited to spatter-coating, but may also be carried out inaccordance with vacuum evaporation, ion plating, metal plating, and thelike.

Subsequently, the disc D is transported into the chamber 10 of theplasma CVD apparatus shown in FIG. 1, and the surface of the disc D isexposed to a reactant gas, which is supplied from the supply source 14through the introduction tube 15 into the chamber 10, from which the gasis exhausted via the exhaust tube 16 to circulate the gas within.

The reactant gas is preferably a mixed gas of hydrocarbon and hydrogen,with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1˜1to 100 by volume. The hydrocarbon preferably comprises at least one typeof hydrocarbon selected from among lower saturated hydrocarbons, lowerunsaturated hydrocarbons, and lower cyclic hydrocarbons.

In this operation, the flow rate of the reactant gas is preferably inthe range of 50˜500 sccm. Additionally, the inner pressure of thechamber 10 is maintained at a predetermined value such as 0.1˜10 Pa.

At the same time, high frequency electrical power of preferably 500˜2000W is supplied to the electrodes 11 to generate plasma, and a carbonprotective film is formed on both sides of the disc D by means of plasmachemical gas phase growth, using the aforementioned reactant gas as astarting material. The thickness of the carbon protective film ispreferably in the range of 30˜100 Å.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode different. By means of making the phases of electrical powersupplied to each electrode 11 different, it is possible to improve boththe coating rate and durability of the protective film. The differencein the phase of electrical power supplied to each electrode ispreferably in the range of 90˜270°, and in particular, the oppositephase (i.e., 180°) is preferred.

It is preferable to form the film while performing bias applying such ashigh frequency bias or pulse D.C. bias to the disc D, using the biaselectrical source 13.

The conditions of bias such as voltage and the like are preferably asdescribed in the aforementioned.

The resultant carbon protective film contains a higher content ofdiamond-like-carbon (DLC), which exhibit an increased hardness.

Additionally, it is possible to provide a lubricating film by means ofapplying the aforementioned lubricant on the protective film.

Examples of the magnetic recording medium manufactured according to theaforementioned manufacturing method may include a magnetic recordingmedium comprising a structure shown in FIG. 2.

In the magnetic recording medium according to this embodiment, anon-magnetic substrate S, a non-magnetic base film 31, a magnetic film32, a carbon protective film 33, and a lubricating film 34 are provided.

According to the aforementioned manufacturing method, a carbonprotective film is formed by, means of a plasma CVD method, after anon-magnetic base film and magnetic film are formed on the substrate S,which has been treated with texture-processing. In this manner, thecarbon protective film contains a high content of DLC, leading to asuperior durability. Accordingly, it is possible to make the carbonprotective film thinner while also maintaining a sufficient durability.

Consequently, the surface of the resultant magnetic recording mediumreflects the surface of the substrate S, wherein the average surfaceroughness (Ra) is in the range of 1˜20 Å, while also maintaining auniform and sufficient difference in height.

Accordingly, it is possible to provide a highly reliable magneticrecording medium exhibiting superior CSS and glide avalanche properties,which is capable of sufficiently increasing the recording densitywithout lowering the output properties thereof.

On the other hand, when the carbon protective film is formed accordingto a conventional spatter-coating method or the like, the thickness ofthe carbon protective film must be increased to a certain extent, fromthe perspective of the resistance to sliding. Therefore, even if theirregularities on the surface of the substrate S are uniform, themicro-irregularities on the surface of the magnetic recording mediumtend to become non-uniform. Moreover, when the average surface roughnessof the substrate S (Ra) is kept low, for example in the range of 1˜20 Å,in order to increase the glide avalanche property, the magnetic headadherence during the CSS operation tends to occur due to the partiallyflat surface of the magnetic recording medium, thus leading to inferiorCSS properties.

In the following, the effects of the present invention are specified,using concrete examples.

TEST EXAMPLE 95

A magnetic recording medium was manufactured using the plasma CVDapparatus and texture-processing equipment shown in FIGS. 1 and 3,respectively. The texture-processing equipment (manufactured by Hitachi)is provided with a controller 26 comprising rubber with an outercircumference of 42 mm and length in axial direction of 42 mm.Additionally, 2501-2 manufactured by Chiyoda (with a thickness of 0.2 mmand width of 38 mm) was used as the abrasive tape A.

An aluminium alloy substrate S coated with a NiP metal film (with adiameter of 95 mm, and thickness of 0.8 mm) was supported by means of asubstrate support member 24 of the texture-processing equipment, androtated at a constant speed of 380 rpm, while the abrasive tape A waspushed against and ran over the substrate S with a pressure of 2 kg/cm².At the same time, the abrasive particle slurry was introduced from theabrasive particle supply nozzle 27, to supply abrasive particles betweenthe abrasive tape A and substrate S.

The receiving speed of the abrasive tape A was set at 0.2 cm/sec.Furthermore, a 20% mixed solution of diamond abrasive particles with aparticle diameter of 0.3 μm was used as the abrasive particle slurry.Additionally, when performing texture-processing, the abrasive tape Awas oscillated at a frequency of 2 Hz and oscillation width of 20 mm, inthe direction perpendicular to the running direction of the tape, bymeans of an oscillation mechanism (not shown).

The average surface roughness (Ra) of the substrate S as a result ofthis texture-processing operation is shown in Table 15.

A non-magnetic base film comprising a Cr alloy (with a thickness of 600Å), and a magnetic film comprising a Co alloy were successively formedon the resultant substrate S by means of DC Magnetron Spattering device(3010 manufactured by Anelva), to form a disc D.

Subsequently, the disc D was transported into the chamber 10 of theplasma CVD apparatus, and a reactant gas was supplied from the supplysource 14 into the chamber to achieve a flow rate of 130 sccm. A mixedgas of toluene and hydrogen, with a mixing ratio of toluene to hydrogenof 1 to 10 by volume, was used as the reactant gas. In addition, theinner pressure of the chamber 10 was maintained at 6 Pa.

At the same time, high frequency electrical power of 500 W was suppliedto the electrodes 11 to generate plasma, and a carbon protective filmwith a thickness of 50 Å was formed on both sides of the disc D. Highfrequency electrical power of 50 W was applied to the disc D, using thebias electrical source 13. Additionally, the difference in the phase ofhigh frequency electrical power supplied to each electrode 11 was set at180°.

Subsequently, a lubricating film with a thickness of 15 Å was formed bymeans of applying a fomblin lubricant onto the carbon protective film,thereby yielding a magnetic recording medium.

The glide avalanche test, and CSS test described in the following wereperformed on the magnetic recording medium.

In the glide avalanche test, the glide avalanche of the magneticrecording medium was measured using a grind tester (DS4200 manufacturedby Sony Techtronics).

In addition, in the CSS test, using an MR head, a CSS operation wasperformed 20000 times at a rotational speed of 7200 rpm, and atemperature of 40° C. with a humidity of 80%. The dynamic stiction valuewas monitored after allowing the magnetic recording medium to sit forone hour. These results are shown in Table 15.

TEST EXAMPLES 96˜99

Magnetic recording media were manufactured, in which the average surfaceroughness (Ra) of the substrate S was modified by means of adjusting theduration time for performing texture-processing.

The glide avalanche test and CSS test were performed on these magneticrecording media. The results are shown in Table 15.

TEST EXAMPLES 100 AND 101

Magnetic recording media were manufactured, in which the average surfaceroughness (Ra) of the substrate S was changed by means of modifying theparticle diameter of the abrasive particles used in texture-processing.

The glide avalanche test and CSS test were performed on these magneticrecording media. The results are shown in Table 15.

TEST EXAMPLE 102

A magnetic recording medium was manufactured in the same manner as inTest Example 96, with the exception that the carbon protective film wasformed according to the spatter-coating method.

The glide avalanche test and CSS test were performed on this magneticrecording medium. The results are shown in Table 15.

TABLE 15 Number of rotation Abrasive Average Oscillation of particlesurface Glide frequency substrate diameter roughness avalanche Stiction(Hz) (rpm) (μm) Ra(Å) (μ inch) (−) Test Example 95 3 380 0.3 9 0.26 0.37Test Example 96 3 450 0.3 17 0.30 0.34 Test Example 97 3 300 0.3 18 0.320.40 Test Example 98 5 300 0.3 20 0.33 0.31 Test Example 99 3 2000 0.312 0.29 0.36 Test Example 100 3 450 1.0 28 0.51 0.36 Test Example 101 3600 1.0 30 0.56 0.39 Test Example 102 3 450 0.3 17 0.40 0.97

From the results shown in Table 15, it is clear that the magneticrecording media manufactured according to the plasma CVD method, whereinthe average surface roughness (Ra) was 1˜20 Å, exhibited sufficientlylow glide avalanche values and stiction values, leading to superior CSSand glide avalanche properties.

As explained in the aforementioned, according to the present invention,it is possible to provide a highly reliable magnetic recording mediumexhibiting superior CSS and glide avalanche properties, which is capableof increasing the recording density sufficiently without lowering theoutput properties thereof.

In the following, another embodiment of the method for manufacturingmagnetic recording medium according to the present invention isdescribed, using an example in which the plasma CVD apparatus shown inFIG. 1 is employed.

Initially, a non-magnetic base film and magnetic film are formed on bothsides of a non-magnetic substrate, according to the spatter-coatingmethod, to obtain a disc D.

The non-magnetic substrate may comprise any substrate that is generallyused as a substrate for magnetic recording medium, as described in theaforementioned.

The surface of the non-magnetic substrate is preferably treated withtexture-processing such as mechanical texture-processing. In particular,the average surface roughness (Ra) is preferably in the range of 1˜20 Å.If the Ra exceeds 20 Å, the grind height property of the resultantmagnetic recording medium is undesirably reduced. The materials andthickness of the non-magnetic base film and magnetic film are asdescribed in the aforementioned.

Subsequently, the disc D, provided with the non-magnetic base film andmagnetic film on the non-magnetic substrate according to theaforementioned operation, is transported into the chamber 10 of theplasma CVD apparatus, and the surface of the disc D is exposed to areactant gas, which is supplied from the supply source 14 through theintroduction tube 15 into the chamber 10. Gas is exhausted via theexhaust tube 16 from chamber 10 to circulate the gas within.

In the manufacturing method according to the present embodiment, thereactant gas is preferably a butadiene gas or a mixed gas of butadieneand hydrogen which mixing ratio of butadiene to hydrogen is preferablyin the range of 100 to 0˜1 to 100 by volume, and more preferably 100 to0˜1 to 25.

If the mixing ratio of butadiene in the aforementioned gas by volume isless than the aforementioned range, the coating rate becomes too low,unsuitable for practical industrial production.

Additionally, when using the aforementioned mixed gas of butadiene andhydrogen as the reactant gas, the mixing ratio of butadiene to hydrogenin the reactant gas is preferably in the range of 100 to 60˜1 to 100,and more preferably 100 to 60˜1 to 25.

When forming the carbon protective film, the inner pressure of thechamber 10 is preferably set at a predetermined value, such as 0.1˜10Pa.

At the same time, high frequency electrical power of preferably 50˜2000W is supplied to the electrodes 11, using the high frequency electricalsource 12, to generate plasma, and a carbon protective film is formed onboth sides of the disc D by means of plasma chemical gas phase growth,using the aforementioned reactant gas as a starting material. Herein,the aforementioned butadiene gas serves as the carbon source for thecarbon protective film.

When supplying electrical power to the electrodes 11 and 11, it ispreferable to make the phases of electrical power supplied to eachelectrode 11 different. By means of making the phases of electricalpower supplied to each electrode 11 different, it is possible to improvethe coating rate and durability of the protective film. The differencein the phase of electrical power supplied to each electrode ispreferably in the range of 90˜270°, and in particular, the oppositephase (i.e., 180°) is preferred.

The thickness of the carbon protective film is in the range of 30˜100 Å,and preferably 30˜75 Å. If the thickness is less than the aforementionedrange, the resistance to corrosion of the resultant carbon protectivefilm is decreased. If the thickness exceeds the aforementioned range,the resultant magnetic recording medium tends to (undesirably) exhibitgreater spacing loss at the time of recording and replay.

At the time of forming the carbon protective film, bias such as highfrequency bias and pulse D.C. bias, is applied to the disc D, using theelectrical bias source 13.

When using high frequency bias as the bias, high frequency electricalsource is used as the bias electrical source 13, and high frequencyelectrical power of 10˜300 W, preferably 10˜150 W, is applied to thedisc D.

If the electrical power is less than the aforementioned range, theresistance to sliding of the resultant carbon protective film isreduced. If the electrical power exceeds the aforementioned range,abnormal discharge tends to occur in the chamber 10 at the time ofcoating, leading undesirably to portions of abnormal growth on thecarbon protective film.

When using pulse D.C. bias as the bias, a pulse D.C. electrical sourceis used as the bias electrical source 13, and a voltage of −400˜−10V,preferably −300˜−50V is applied to the disc D.

If the voltage is less than the aforementioned range, resistance tosliding of the obtained, carbon protective film is reduced. If itexceeds the aforementioned range, abnormal discharge tends to occur inthe chamber 10 during coating, leading undesirably to portions ofabnormal growth on the carbon protective film.

Additionally, the pulse width of the aforementioned pulse D.C. bias ispreferably in the range of 10˜50000 ns, and the frequency is preferablyin the range of 10 kHz˜1 GHz.

By means of performing bias applying, the carbon protective filmcontains a higher content of diamond-like-carbon (DLC), which exhibitboth an increased hardness and superior strength.

Additionally, a lubricating film may be provided on the protective film,by means of applying the aforementioned lubricant.

In the aforementioned manufacturing method, by means of using abutadiene gas, or a mixed gas of butadiene and hydrogen, which mixingratio of butadiene to hydrogen is in the range of 100 to 0˜1 to 100 byvolume, as the reactant gas, at the time of forming the carbonprotective film, it is possible to form a carbon protective film with asuperior durability. As a result, it is possible to make the carbonprotective thinner while maintaining the durability, and to provide amagnetic recording medium that is capable of reducing spacing loss.

Consequently, it is possible to provide a highly reliable magneticrecording medium, which is capable of sufficiently increasing therecording density without lowering the output properties thereof.

Additionally, by means of performing bias applying to the disc D at thetime of forming the carbon protective film, the carbon protective filmcontains a higher content of DLC, leading to a superior strength. Inaddition, it is also possible to improve the coating rate, leading to anefficient production.

The reason that the carbon protective film with a superior durabilitycan be provided by means of using a butadiene gas, or a mixed gas ofbutadiene and hydrogen, which mixing ratio of butadiene to hydrogen isin the range of 100 to 0˜1 to 100 by volume, as the reactant gas whenforming the aforementioned carbon protective film, is unclear. However,this may be attributable to the fact that the resultant carbonprotective film contains a higher content of DLC which exhibit anexcellent hardness, and thus displays an overall superior strength, bymeans of using the aforementioned gas as the reactant gas.

A mixed gas wherein other gases such as nitrogen, argon, oxygen,fluorine, and the like, are added into the aforementioned butadiene gas,or mixed gas of butadiene and hydrogen at a mixing ratio of for example1˜100 vol %, may be also used as the reactant gas.

In addition, a mixed gas wherein other gases, which may serve as acarbon source, such as methane, ethane, ethylene, propylene, butylene,butane, benzene, toluene, and the like, are mixed into butadiene gas ata mixing ratio of, for example, 1˜100 vol %, may be used instead of theaforementioned butadiene gas.

In addition, in the aforementioned manufacturing method according to thepresent embodiment, a carbon protective film is formed according only toa plasma CVD method. However, the method for manufacturing magneticrecording medium according to the present invention is not limitedthereto, and a protective film may also comprise a multilayer structurecomprising a plasma carbon layer formed according to the plasma CVDmethod, and a layer formed according to another method, such as aspatter-carbon layer and/or tantalic nitride layer formed according tothe spattering method.

In the following, the effects of the present invention are specified,using concrete examples.

TEST EXAMPLE 103˜117

After an aluminium alloy substrate coated with a NiP metal film (with adiameter of 95 mm and thickness of 0.8 mm) was treated with mechanicaltexture-processing to form an average surface roughness of 20 Å, anon-magnetic base film (with a thickness of 600 Å) comprising a Cralloy, and a magnetic film comprising a Co alloy were successivelyformed on both sides of the substrate S, using DC Magnetron SpatterEquipment (3010 manufactured by Anelva), to obtain a disc D.

Subsequently, the disc D was transported into the chamber 10 of theplasma CVD apparatus, and the reactant gas was supplied from the supplysource 14 inside of the chamber.

At the same time, high frequency electrical power of 700 W (with afrequency of 13.56 MHz) was supplied to the electrodes 11, to generateplasma, and a carbon protective film with a thickness of 50 Å was formedon both sides of the disc D.

The temperature of the disc D when forming the carbon protective filmwas set at 160° C. The distance between the electrodes 11 and disc D wasset at 30 mm. The inner pressure of the chamber was maintained at 2 Pa.

The type and flow rate of the reactant gas, type and power of biasapplied to the disc D by means of the bias electrical source 13,difference in the phase of high frequency electrical power supplied tothe electrodes 11, thickness of the formed carbon protective film, andcoating rate are shown in Table 16.

Subsequently, a lubricating film with a thickness of 20 Å was formed onthe carbon protective film by means of applying a fomblin lubricant,thereby yielding a magnetic recording medium.

The CSS test, corrosion test, and Raman spectral analysis described inthe following were performed on the resultant magnetic recording media.

In the CSS test, using an MR head, a CSS operation was performed 20000times at a rotational speed of 7200 rpm, and a temperature of 40° C.with a humidity of 80%. The dynamic stiction value was monitored afterallowing the magnetic recording medium to sit for one hour.

In the corrosion test, after being allowed to sit for 96 hours at a hightemperature (60° C.) and a high humidity (80%), the magnetic recordingmedium was soaked in 50 cc of ultrapure water at 25° C., and theextraction amount of Co (per substrate area) was measured. In addition,after being allowed to sit for 96 hours at a normal temperature (25° C.)and normal humidity (50%), the extraction amount of Co was measured inthe same manner.

In the Raman spectral analysis, Raman spectral analysis (argon ion laserexcitation) was performed, using a Raman spectral analysis apparatus(manufactured by JEOL). The results are shown in Table 17.

In the table, “RF” represents high frequency. Furthermore, “RF phasedifference” represents the difference in the phase of electrical powersupplied to two electrodes 11 and 11.

TABLE 16 Reactant gas Ratio of Carbon source gas Hydro- butadiene RFProtec- Coat- Flow gen flow in reactant phase tive film ing rate rategas Bias differ- thick- rate Type (sccm) (sccm) (vol. %) Bias power ence(°) ness (Å) (Å/min) Test Ex 103 Buta- 6 120 4.8 Pulse −200 V 180 50 218diene D.C. Test Ex 104 Buta- 30 200 13.0 Pulse −200 V 180 50 285 dieneD.C. Test Ex 105 Buta- 30 120 20.0 Pulse −200 V 180 50 533 diene D.C.Test Ex 106 Buta- 30 120 20.0 RF 30 W 180 50 506 diene Test Ex 107 Buta-25 60 29.4 Pulse −200 V 180 50 552 diene D.C. Test Ex 108 Buta- 30 2060.0 Pulse −200 V 180 50 689 diene D.C. Test Ex 109 Buta- 30 0 100 Pulse−200 V 180 50 810 diene D.C. Test Ex 110 Buta- 3 120 2.4 Pulse −200 V180 50 165 diene D.C. Test Ex 111 Buta- 30 120 20.0 None — 180 50 386diene Test Ex 112 Buta- 30 120 20.0 Pulse −200 V 0 50 185 diene D.C.Test Ex 113 Buta- 30 120 20.0 Pulse −200 V 180 20 533 diene D.C. Test Ex114 Methane 60 60 — Pulse −200 V 180 50 324 D.C. Test Ex 115 Ethane 1000 — Pulse −200 V 180 50 385 D.C. Test Ex 116 Ethylene 60 60 — Pulse −200V 180 50 308 D.C. Test Ex 117 Acetone 100 0 — Pulse −200 V 180 50 221D.C.

TABLE 17 Corrosion test Normal temp. & High temp. & Stiction normalhumidity high humidity Raman spectral analysis (−) (μg/disc) (μg/disc)åG-line (cm⁻¹) Id/Ig (−) Test Example 103 0.64 0.05 0.11 0.44 1540.5Test Example 104 0.81 0.07 0.17 0.38 1536.7 Test Example 105 0.43 0.080.22 0.37 1538.2 Test Example 106 0.60 0.04 0.16 0.40 1536.4 TestExample 107 0.96 0.08 0.20 0.36 1534.8 Test Example 108 0.77 0.08 0.240.35 1533.9 Test Example 109 0.71 0.08 0.18 0.34 1533.8 Test Example 1100.88 0.07 0.13 0.48 1541.2 Test Example 111 Crash 0.36 0.99 no peak —Test Example 112 0.56 0.21 0.77 0.75 1539.5 Test Example 113 1.23 0.782.57 — — Test Example 114 2.25 0.11 0.45 1.02 1558.0 Test Example 115Crash 0.14 0.58 0.35 1559.6 Test Example 116 2.12 0.16 0.36 — — TestExample 117 Crash 0.23 0.74 — —

From the results shown in Tables 16 and 17, it is clear that themagnetic recording media manufactured according to the method whereinbias was applied to the disc D at the time of coating, and butadiene gasor a mixed gas of butadiene and hydrogen, with a mixing ratio ofbutadiene to hydrogen of 100 to 0˜1 to 100 by volume, exhibited lowerstiction values, leading to a superior resistance to the CSS operation.Additionally, it is clear that the coating rate improved.

In addition, from the results of the corrosion test, the aforementionedmagnetic recording media displayed an extremely small amount ofcorrosion, and exhibited a resistance to corrosion to a degree whichposes no problems from practical use.

Additionally, from the results of the Raman spectral analysis, theaforementioned magnetic recording medium exhibited a G-band peak of arelatively higher frequency, a low Id/Ig, and a high DLC content.

In addition, the magnetic recording medium manufactured according to themethod wherein the difference in the phase of high frequency electricalpower supplied to the electrodes 11 was 180 degrees, resulted in animprovement in the coating rate, compared to those with no difference inthe phase.

As explained in the aforementioned, according to the method formanufacturing magnetic recording medium according to the presentinvention, it is possible to form a carbon protective film with asuperior durability. As a result, it is possible to make the carbonprotective film thinner while also maintaining a sufficient durability,and thereby reduce spacing loss.

Accordingly, it is possible to provide a highly reliable magneticrecording medium which is capable of sufficiently increasing therecording density without lowering the output properties thereof.Additionally, it is possible to increase the coating rate, leading to anefficient production.

INDUSTRIAL APPLICABILITY

The magnetic recording medium and method for manufacturing the sameaccording to the present invention may be applied to a magneticrecording medium (and manufacturing method for the same), such asmagnetic disc or the like, which is used in magnetic disc equipment.

What is claimed is:
 1. A method for manufacturing a magnetic recordingmedium comprising the steps of forming a carbon protective film onto adisc, the non-magnetic substrate of which is layered with a non-magneticbase film and magnetic film, using a reactant gas containing carbonatoms as a starting material, according to a plasma CVD method, whereina mixed gas of hydrocarbon and hydrogen, in which the mixing ratio ofhydrocarbon to hydrogen is in the range of 2 to 1˜1 to 100 by volume, isused as a reactant gas, while applying a bias to said disc.
 2. A methodfor manufacturing a magnetic recording medium according to claim 1,wherein toluene is used as said hydrocarbon.
 3. A method formanufacturing a magnetic recording medium according to claim 2, whereina mixed gas of toluene and hydrogen, in which the mixing ratio oftoluene and hydrogen is in the range of 1 to 15˜1 to 20 by volume, isused as said reactant gas.
 4. A method for manufacturing a magneticrecording medium according to one of claims 1˜3, wherein said carbonprotective film is formed according to a plasma CVD method, under highfrequency electrical discharge.
 5. A method for manufacturing a magneticrecording medium according to claim 4 wherein the phases of electricalpower, supplied to each electrode arranged on the respective sides ofsaid disc, are different from each other at the time of forming saidcarbon protective film simultaneously, on both sides of said disc, underhigh frequency electrical discharge.
 6. A method for manufacturing amagnetic recording medium according to one of claims 1˜3, wherein highfrequency bias is used as said bias.
 7. A method for manufacturing amagnetic recording medium according to claim 6 wherein said carbonprotective film is formed according to a plasma CVD method, under highfrequency electrical discharge.
 8. A method for manufacturing a magneticrecording medium according to claim 7, wherein the phases of electricalpower, supplied to each electrode arranged on the respective sides ofsaid disc, are different from each other, at the time of forming saidcarbon protective film simultaneously, on both sides of said disc, underhigh frequency electrical discharge.